Grapefruit Rosemary Olive Oil Upside‑Down Polenta Cake

Why You’ll Love This Recipe

• Sunshine on a plate: bittersweet grapefruit wheels glazed in rosemary-citrus caramel.
• Olive oil and yogurt keep the polenta crumb tender, moist, and fragrant.
• Upside-down finish looks bakery-fancy but uses one skillet or cake pan.
• Balanced sweetness with a gentle herbal note that lets the citrus shine.

Grocery List

• Produce: 2 large ruby red grapefruits, 1 small orange (optional), fresh rosemary (1 small bunch)
• Dairy: 1 cup full-fat Greek yogurt, 3 large eggs
• Pantry: Extra-virgin olive oil, granulated sugar, light brown sugar, all-purpose flour, fine yellow cornmeal, baking powder, baking soda, vanilla extract, fine sea salt, honey (optional)

Full Ingredients

Caramelized Citrus Layer

• 2 large ruby red grapefruits, peeled and cut into 1/4-inch rounds (remove seeds)
• 1 small blood orange or navel orange, peeled and sliced (optional, for color)
• 1/2 cup (110 g) light brown sugar, packed
• 3 tablespoons extra-virgin olive oil
• 2 tablespoons freshly squeezed grapefruit juice
• 1 small rosemary sprig (about 3 inches) or 1/2 teaspoon finely chopped rosemary
• Pinch fine sea salt

Polenta Cake Batter

• 3/4 cup (105 g) fine yellow cornmeal (polenta)
• 1 cup (130 g) all-purpose flour
• 1 1/2 teaspoons baking powder
• 1/2 teaspoon baking soda
• 3/4 teaspoon fine sea salt
• 1 cup (240 g) full-fat plain Greek yogurt, at room temperature
• 2 tablespoons freshly squeezed grapefruit juice
• 2/3 cup (135 g) granulated sugar
• Finely grated zest of 1 large grapefruit (about 1 tablespoon)
• 1 tablespoon finely chopped fresh rosemary
• 1/2 cup (120 ml) extra-virgin olive oil
• 2 teaspoons pure vanilla extract
• 3 large eggs, at room temperature

Finishing (Optional but Lovely)

• 1 tablespoon honey
• 1 tablespoon freshly squeezed grapefruit juice
• Small rosemary tips/leaves, for garnish
• Pinch flaky sea salt, for finishing

Step-by-Step Instructions

Step 1: Heat the oven and prep the pan

Preheat the oven to 350°F (175°C). Use a 9-inch oven-safe skillet (cast iron works beautifully) or a 9-inch round cake pan with 2-inch sides. If using a cake pan, lightly oil the sides and line the bottom with a round of parchment; lightly oil the parchment as well. Avoid using a springform pan (caramel can leak).

Step 2: Prep and dry the citrus

Slice a thin cap from the top and bottom of each grapefruit. Stand the fruit upright and cut away the peel and pith, following the curve of the fruit. Slice into 1/4-inch rounds and remove seeds. Do the same with the optional orange. Lay slices on a double layer of paper towels and blot the tops dry—drier fruit makes a glossier top and prevents sogginess.

Step 3: Make the rosemary–grapefruit caramel and arrange the wheels

In your skillet (or a small saucepan if using a cake pan), combine the brown sugar, 3 tablespoons olive oil, 2 tablespoons grapefruit juice, rosemary sprig, and a pinch of salt. Cook over medium heat, stirring until smooth and bubbling, 2–3 minutes. Remove the rosemary sprig. If using a saucepan, immediately pour the caramel into the prepared cake pan and tilt to coat the bottom evenly. Arrange the citrus slices tightly in a single layer over the caramel (they will shrink slightly as they bake); it is fine if they overlap a bit.

Step 4: Bloom the cornmeal and build the citrus sugar

In a medium bowl, stir the yogurt with 2 tablespoons grapefruit juice. Add the cornmeal, mix well, and let it sit 10 minutes to soften. Meanwhile, in a large bowl, rub the grapefruit zest into the granulated sugar with your fingertips until the sugar is fragrant and slightly moist—this releases essential oils for bigger citrus flavor.

Step 5: Mix the batter

Whisk the eggs into the zested sugar until thick and pale, then whisk in 1/2 cup olive oil, vanilla, and the chopped rosemary. In a separate bowl, whisk the flour, baking powder, baking soda, and salt. Stir the dry ingredients into the egg mixture until just combined. Fold in the cornmeal–yogurt mixture until no dry spots remain. The batter will be thick and creamy.

Step 6: Bake

Scrape the batter over the citrus, spreading gently to the edges without disturbing the slices. Bake until the top is golden, the center springs back, and a tester inserted into the cake (not the citrus) comes out clean, 40–45 minutes. If the top is browning too quickly, tent loosely with foil for the last 10 minutes.

Step 7: Invert, glaze, and garnish

Cool the cake in the pan on a rack for 15 minutes. Run a thin knife around the edge to loosen. Place a serving plate over the pan and carefully invert; lift off the pan and peel away parchment if used. For a glossy finish, warm the honey with 1 tablespoon grapefruit juice and brush lightly over the citrus. Garnish with tiny rosemary leaves and a whisper of flaky sea salt. Let the cake set 10–15 minutes before slicing.

Pro Tips

• Blooming the cornmeal in yogurt softens the grit and gives a tender, sunny crumb—don’t skip the 10-minute rest.
• Blot citrus slices very dry before arranging to prevent watery caramel.
• Rub zest into sugar to extract fragrant oils for a brighter grapefruit flavor.
• Cast iron makes caramel easy, but a lined 9-inch cake pan works too. Avoid springform pans to prevent leaks.
• For clean slices, let the cake sit 15–20 minutes after inverting so the caramel sets slightly.

Variations

• Citrus medley: Mix grapefruit with blood orange and Meyer lemon slices for a sunset mosaic.
• Gluten-free: Use a cup-for-cup gluten-free flour blend in place of all-purpose flour; keep cornmeal amount the same.
• Dairy-free: Swap Greek yogurt for a thick, unsweetened plant-based yogurt and skip the honey glaze or use agave.

Storage & Make-Ahead

Store covered at room temperature for up to 2 days or refrigerate up to 4 days. For longer storage, wrap slices well and freeze up to 2 months; thaw at room temperature. To refresh, warm slices in a 300°F (150°C) oven for 8–10 minutes to loosen the caramel and revive the crumb. The caramelized citrus can be arranged in the pan up to 2 hours ahead; keep at room temperature.

Nutrition (per serving)

Approximate values for 1 of 10 slices: 330 calories; 18 g fat; 40 g carbohydrates; 24 g sugars; 5 g protein; 230 mg sodium; 1 g fiber.