One-Bowl Chocolate Snack Cake with Fudge Frosting

Why You’ll Love This Recipe

• One-bowl batter means minimal dishes and maximum chocolate flavor.
• Sour cream keeps the cake incredibly moist and tender for days.
• Thick, glossy fudge frosting spreads like a dream and sets softly.
• Cheerful sprinkles make it weeknight-easy yet celebration-worthy.

Grocery List

• Produce: None
• Dairy: Sour cream, unsalted butter, eggs, milk (optional for frosting)
• Pantry: All-purpose flour, granulated sugar, powdered sugar, Dutch-process cocoa powder, baking powder, baking soda, fine sea salt, vanilla extract, neutral oil, brewed coffee (or water), rainbow sprinkles

Full Ingredients

For the one-bowl chocolate sour cream cake

• 1 1/4 cups (150 g) all-purpose flour
• 1 cup (200 g) granulated sugar
• 1/2 cup (45 g) Dutch-process cocoa powder
• 1 teaspoon baking soda
• 1/2 teaspoon baking powder
• 1/2 teaspoon fine sea salt
• 2 large eggs, at room temperature
• 3/4 cup (180 g) full-fat sour cream
• 1/3 cup (75 g) neutral oil (such as canola or vegetable)
• 1/2 cup (120 ml) hot brewed coffee (or hot water)
• 2 teaspoons vanilla extract

For the thick fudge frosting and finish

• 1/2 cup (113 g) unsalted butter
• 1/2 cup (45 g) Dutch-process cocoa powder
• 2 1/2 cups (300 g) powdered sugar, sifted
• 1/4 cup (60 g) full-fat sour cream
• 1 teaspoon vanilla extract
• 1/8 teaspoon fine sea salt
• 1–3 tablespoons (15–45 ml) hot brewed coffee or milk, as needed for consistency
• 3 tablespoons rainbow sprinkles

Step-by-Step Instructions

Step 1: Prep the pan and oven

Heat the oven to 350°F (177°C). Grease an 8-inch square metal pan and line it with a parchment sling (two strips that overhang) for easy removal. Lightly grease the parchment as well.

Step 2: Whisk the dry ingredients

In a large mixing bowl (this is your only bowl for the cake), whisk together the flour, sugar, cocoa, baking soda, baking powder, and salt until the mixture looks uniform and lump-free. This prevents dry pockets later.

Step 3: Add the wet ingredients (except the hot liquid)

Add the eggs, sour cream, oil, and vanilla directly to the bowl. Whisk until almost smooth; a few small streaks of flour are fine. Do not overmix at this stage—just bring it together.

Step 4: Bloom with hot coffee and finish the batter

Stream in the hot brewed coffee (or hot water) while whisking. The heat helps bloom the cocoa, deepening flavor and creating a glossy, pourable batter. Scrape the bowl and whisk once more to ensure it is evenly combined.

Step 5: Bake the cake

Pour the batter into the prepared pan and smooth the top. Bake for 28–33 minutes, until the center springs back lightly and a toothpick inserted near the center comes out with a few moist crumbs. Do not overbake.

Step 6: Cool completely

Cool the cake in the pan on a rack for 15 minutes. Use the parchment to lift the cake out and let it cool completely on the rack, about 45–60 minutes, before frosting.

Step 7: Make the thick fudge frosting, frost, and sprinkle

In a medium bowl, melt the butter until just liquefied and warm, not sizzling. Whisk in the cocoa until smooth and shiny. Add the powdered sugar, sour cream, vanilla, and salt. Beat with a whisk or hand mixer until thick and creamy, drizzling in 1–3 tablespoons hot coffee or milk until it becomes spreadable but still dense. Spread generously over the cooled cake, creating swoops. Top evenly with 3 tablespoons rainbow sprinkles. Slice into 12 squares and serve.

Pro Tips

• Use Dutch-process cocoa for the deepest chocolate color and classic fudge flavor; natural cocoa also works but will be a touch lighter.
• Hot coffee intensifies chocolate; hot water works too if you prefer to avoid coffee.
• Weigh your flour for best texture. If measuring by volume, fluff, spoon, and level to avoid a dense cake.
• Frost while the cake is completely cool to keep the frosting thick, not melty.
• For the cleanest slices, chill the frosted cake 15 minutes to set, then cut with a warm knife, wiping between cuts.

Variations

• Double It for a 9×13 Pan: Double all ingredients, bake at 350°F (177°C) for 32–38 minutes.
• Cupcakes: Divide batter among 12 lined wells and bake 18–20 minutes; frost as directed.
• Add-Ins: Fold 1/2 cup mini chocolate chips or 1 teaspoon finely grated orange zest into the batter for a twist.

Storage & Make-Ahead

Store the frosted cake covered at cool room temperature for up to 2 days, or refrigerate up to 5 days (bring to room temp before serving for the softest crumb). To freeze, wrap unfrosted cake tightly and freeze up to 2 months; thaw at room temp, then frost and add sprinkles just before serving. The frosting can be made up to 3 days ahead and refrigerated; bring to room temp and beat in a splash of hot coffee or milk to loosen before spreading.

Nutrition (per serving)

Approximate for 1 of 12 squares: 400 calories; 18 g fat; 54 g carbohydrates; 4 g protein; 230 mg sodium; 39 g sugars.