Brown Butter Cornflake Marshmallow Crunch Cookies

Quick Recipe Version (TL;DR)

• Yield: About 24 cookies
• Prep Time: 30 minutes (plus 30 minutes chilling)
• Cook Time: 12–14 minutes per batch
• Total Time: About 1 hour 15 minutes

Quick Ingredients

• 3 cups cornflakes cereal
• 4 tbsp (55 g) unsalted butter, melted (for cornflake crunch)
• 3 tbsp granulated sugar + 1/2 tsp kosher salt
• 1 cup (2 sticks, 226 g) unsalted butter, for browning
• 1 1/2 cups packed light brown sugar
• 1/2 cup granulated sugar
• 2 large eggs, room temperature
• 2 tsp pure vanilla extract
• 2 1/4 cups (270 g) all-purpose flour
• 1 tsp baking soda + 3/4 tsp fine salt
• 1 1/2–2 cups Cornflake Crunch, roughly crushed
• 1 1/2 cups mini marshmallows
• Flaky sea salt, for finishing (optional but recommended)

Do This

• 1. Heat oven to 300°F (150°C). Toss cornflakes with melted butter, sugar, and salt; bake 12–15 minutes until toasty and crisp. Cool completely.
• 2. Brown 1 cup butter on the stove until deep golden and nutty; cool to room temperature until slightly thickened but still pourable.
• 3. Heat oven to 350°F (180°C). Line baking sheets with parchment. Whisk flour, baking soda, and fine salt together.
• 4. Beat browned butter with brown and white sugars until glossy. Mix in eggs and vanilla.
• 5. Add dry ingredients just until combined, then fold in 1 1/2–2 cups crushed Cornflake Crunch.
• 6. Melt mini marshmallows briefly, dollop over dough, and fold only 2–3 times to create ribbons. Scoop 2-tbsp mounds, spacing well.
• 7. Bake 12–14 minutes until edges are deep golden and centers look just set. While warm, sprinkle flaky sea salt and extra crunch on top. Cool completely.

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Why You’ll Love This Recipe

• Browned butter adds a deep, nutty caramel flavor that makes these cookies taste bakery-level special.
• Crushed cornflakes bake into a crispy, toasty crunch that contrasts beautifully with the chewy centers.
• Melty marshmallow ribbons create gooey pockets and caramelized edges for a nostalgic, cereal-bar-meets-cookie vibe.
• Sweet-salty balance: a hint of salt and optional flaky sea salt finish keep these cookies from ever tasting too sweet.

Grocery List

• Produce: None needed
• Dairy: Unsalted butter, large eggs
• Pantry: Cornflakes cereal, all-purpose flour, light brown sugar, granulated sugar, kosher salt, fine sea salt, flaky sea salt (optional), baking soda, pure vanilla extract, mini marshmallows

Full Ingredients

Cornflake Crunch

• 3 cups (about 90 g) cornflakes cereal
• 4 tbsp (55 g) unsalted butter, melted
• 3 tbsp (38 g) granulated sugar
• 1/2 tsp kosher salt

Browned Butter Cookie Dough

• 1 cup (2 sticks, 226 g) unsalted butter, cut into pieces (for browning)
• 1 1/2 cups (300 g) packed light brown sugar
• 1/2 cup (100 g) granulated sugar
• 2 large eggs, at room temperature
• 2 tsp pure vanilla extract
• 2 1/4 cups (270 g) all-purpose flour, spooned and leveled
• 1 tsp baking soda
• 3/4 tsp fine sea salt or table salt
• 1 1/2–2 cups (about 75–100 g) Cornflake Crunch, roughly crushed (from above; plus extra for topping if desired)

Marshmallow Ribbons & Finishing

• 1 1/2 cups (about 75 g) mini marshmallows
• 1 tsp unsalted butter (for melting with the marshmallows)
• Flaky sea salt, for sprinkling on baked cookies (optional but recommended)

Step-by-Step Instructions

Step 1: Make the Cornflake Crunch

Preheat your oven to 300°F (150°C). Line a baking sheet with parchment paper. In a medium bowl, lightly crush the cornflakes with your hands so you have a mix of smaller pieces and a few larger flakes; you do not want fine crumbs. Drizzle the melted butter over the cornflakes, then sprinkle on the granulated sugar and kosher salt.

Toss gently until all the cornflakes are evenly coated and look slightly glossy. Spread them in a single layer on the prepared baking sheet. Bake for 12–15 minutes, stirring once halfway through, until the cornflakes smell toasty and are a deeper golden color. They will crisp further as they cool. Let the Cornflake Crunch cool completely on the tray, then roughly crush again so you have bite-size pieces. Set aside.

Step 2: Brown the Butter

While the cornflake crunch bakes, brown the butter. Place the 1 cup (226 g) unsalted butter in a light-colored saucepan over medium heat. Melt, then continue to cook, stirring frequently, as it foams. After a few minutes, the foam will subside and you will see browned milk solids forming on the bottom of the pan. Keep stirring until the butter smells nutty and the bits on the bottom are a deep golden brown, 5–8 minutes total.

Immediately pour the browned butter and all the browned bits into a heatproof bowl to stop the cooking. Let cool at room temperature until just slightly warm and beginning to thicken but still pourable, about 20–30 minutes. This step is important; if the butter is hot, it can make the dough greasy and cause the cookies to overspread.

Step 3: Prepare the Dry Ingredients and Pans

Increase the oven temperature to 350°F (180°C). Line two large baking sheets with parchment paper (parchment is essential here because melted marshmallow can stick to bare pans). In a medium bowl, whisk together the all-purpose flour, baking soda, and fine sea salt until well combined. Set aside.

Have your cooled Cornflake Crunch nearby, as you will fold it into the dough later. If your kitchen is warm, you can even pop the crunch into the refrigerator for 5 minutes so it stays extra crisp.

Step 4: Mix the Browned Butter Cookie Dough

In a large mixing bowl (or the bowl of a stand mixer fitted with the paddle attachment), combine the cooled browned butter, light brown sugar, and granulated sugar. Beat on medium speed for 2–3 minutes, scraping down the sides of the bowl as needed, until the mixture looks slightly lighter, glossy, and well combined.

Add the eggs one at a time, mixing well after each addition, then mix in the vanilla extract. The mixture should look smooth and slightly thickened. Add the flour mixture all at once and mix on low speed just until no dry streaks of flour remain. Do not overmix at this stage; you want tender, chewy cookies.

Step 5: Fold in the Cornflake Crunch and Chill

Use a spatula to fold 1 1/2–2 cups of the cooled, roughly crushed Cornflake Crunch into the dough. Start with 1 1/2 cups and add more if you like a very crunchy cookie. Fold gently to distribute the pieces evenly without crushing them completely.

Cover the bowl and chill the dough in the refrigerator for about 30 minutes. This brief chill helps the browned-butter dough firm up, so the cookies bake up thick and chewy instead of spreading too thin. The dough should feel cool and scoopable but not rock-hard.

Step 6: Create Marshmallow Ribbons in the Dough

Place the mini marshmallows and 1 teaspoon butter in a microwave-safe bowl. Microwave on high in 10–15 second bursts, stirring between each, just until the marshmallows are soft, glossy, and starting to melt together but not fully liquefied. You are aiming for a thick, stretchy mixture rather than a smooth sauce.

Retrieve the chilled dough. Dollop the warm marshmallow mixture over the surface of the dough in 4–5 small mounds. Using a spatula, fold the dough over itself only 2–3 times, turning the bowl as you go. You want visible streaks and ribbons of marshmallow running through the dough. Do not fully mix it in; overmixing will cause the marshmallow to disappear into the dough instead of forming gooey pockets.

Step 7: Scoop, Bake, and Finish

Using a 2-tablespoon cookie scoop or heaping tablespoon, portion the dough onto the prepared baking sheets, spacing the mounds at least 2 1/2 inches (6 cm) apart to allow for spreading and marshmallow melt. If you like, press a few extra pieces of Cornflake Crunch gently onto the tops of each scoop for a prettier, crunchier surface.

Bake one sheet at a time on the center rack for 12–14 minutes, or until the edges are deeply golden and crispy-looking, the tops are lightly golden, and the centers look just set but still slightly soft. The marshmallow ribbons will puff and melt, creating caramelized, crinkly patches around the edges.

As soon as the cookies come out of the oven, while they are still hot and soft, sprinkle the tops lightly with flaky sea salt and an extra pinch of Cornflake Crunch if desired. Let the cookies cool on the baking sheet for at least 10 minutes to set before transferring carefully to a wire rack to cool completely. The marshmallow bits are very hot when fresh from the oven; cooling helps them firm into chewy, toffee-like pockets.

Pro Tips

• Watch the butter closely when browning. Use a light-colored pan and stay nearby; browned butter goes from perfect to burnt quickly. Pull it as soon as the bits on the bottom are a deep golden brown and very fragrant.
• Do not skip chilling the dough. Because this dough starts with melted browned butter, chilling is what keeps the cookies thick, chewy, and not overly spread out.
• Keep the marshmallow ribbons chunky. Only fold the melted marshmallow into the dough a few times. Visible streaks and pockets are what give you that signature gooey, crispy-chewy texture.
• Use parchment paper. Marshmallow can glue itself to bare metal. Parchment (or a silicone mat) ensures the cookies release cleanly and the caramelized edges stay intact.
• Pull them while the centers are still soft. The cookies will continue to firm up as they cool. For maximum chew, err on the side of slightly underbaking the centers.

Variations

• Chocolate-chunk version: Fold 1 cup (170 g) chopped dark or milk chocolate into the dough along with the Cornflake Crunch for a s’mores-adjacent cookie with pools of melted chocolate.
• Peanut butter twist: Replace 1/2 cup (60 g) of the flour with 1/2 cup (130 g) creamy peanut butter. Beat the peanut butter in with the browned butter and sugars, then proceed with the recipe for a salty-sweet peanutty variation.
• Cinnamon cereal vibe: Add 1 tsp ground cinnamon to the dry ingredients and a pinch more salt for cookies that taste like a grown-up version of cinnamon breakfast cereal bars.

Storage & Make-Ahead

Store completely cooled cookies in an airtight container at room temperature for up to 4 days. They will be crispiest on day 1–2 and gradually become chewier as they sit. To restore some crisp edges, warm a cookie in a 300°F (150°C) oven for 3–4 minutes.

For longer storage, freeze baked cookies in a single layer until solid, then transfer to a freezer bag or airtight container for up to 2 months. Thaw at room temperature or briefly warm in the oven.

To make ahead, prepare the dough through folding in the Cornflake Crunch (before adding melted marshmallows). Refrigerate up to 24 hours. When ready to bake, let the dough sit at room temperature just until scoopable, then proceed with the marshmallow ribbon step and baking. You can also scoop the dough (after adding marshmallows), freeze the dough balls on a tray until firm, then bake from frozen, adding 1–2 extra minutes to the bake time.

Nutrition (per serving)

Approximate values per cookie (1 of 24): about 210 calories, 11 g fat, 27 g carbohydrates, 1 g fiber, 16 g sugar, and 3 g protein. These numbers are estimates and will vary based on the exact brands and amounts used, and on cookie size.