One-Bowl Chocolate Sheet Cake with Silky Fudge Icing

Why You’ll Love This Recipe

• True one-bowl batter with zero fuss and minimal cleanup.
• Hot coffee deepens the chocolate flavor without tasting like coffee.
• Sour cream keeps the crumb incredibly tender and moist for days.
• Silky stovetop fudge icing glides over the warm cake for a glossy, crackly set.

Grocery List

• Produce: None (optional: fresh berries for serving)
• Dairy: Sour cream, unsalted butter, whole milk, eggs
• Pantry: All-purpose flour, granulated sugar, powdered sugar, unsweetened cocoa powder, baking powder, baking soda, fine sea salt, neutral oil, vanilla extract, coffee beans/ground coffee, optional light corn syrup, optional pecans, optional flaky sea salt

Full Ingredients

For the Chocolate Sheet Cake

• 2 cups (240 g) all-purpose flour
• 1 3/4 cups (350 g) granulated sugar
• 3/4 cup (75 g) unsweetened cocoa powder (natural or Dutch-process)
• 1 1/2 teaspoons baking powder
• 1 1/2 teaspoons baking soda
• 1 teaspoon fine sea salt
• 2 large eggs, at room temperature
• 1 cup (240 g) sour cream, at room temperature
• 1/2 cup (120 ml) neutral oil (canola or vegetable)
• 2 teaspoons vanilla extract
• 1 cup (240 ml) hot brewed coffee

For the Silky Stovetop Fudge Icing

• 1/2 cup (113 g) unsalted butter
• 1/3 cup (30 g) unsweetened cocoa powder
• 6 tablespoons (90 ml) whole milk (or evaporated milk for extra richness)
• 3 cups (360 g) powdered sugar, sifted
• 1 teaspoon vanilla extract
• 1/8 teaspoon fine sea salt
• Optional for gloss: 1 tablespoon light corn syrup
• Optional topping: 1/2 cup toasted chopped pecans, flaky sea salt for finishing

Step-by-Step Instructions

Step 1: Preheat and Prep the Pan

Heat the oven to 350°F (175°C). Lightly grease a 9×13-inch metal baking pan with butter or nonstick spray. Line the bottom with a sheet of parchment paper, leaving two short overhangs for easy lifting, then lightly grease the parchment.

Step 2: Whisk the Dry Ingredients

In a large mixing bowl (your only bowl), whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until evenly combined and no cocoa lumps remain. This ensures even leavening and a smooth, chocolatey crumb.

Step 3: Add Eggs, Sour Cream, Oil, and Vanilla

Add the eggs, sour cream, oil, and vanilla directly to the dry mixture. Whisk just until the mixture looks uniform and creamy with no dry pockets. Avoid overmixing here; a few small lumps are fine.

Step 4: Stream in the Hot Coffee

While whisking, slowly pour in the hot brewed coffee. The batter will loosen and become glossy and thin—that is what you want. Hot coffee blooms the cocoa for deeper flavor and helps smooth the batter.

Step 5: Bake

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 in the center comes out with a few moist crumbs (not wet batter). Set the pan on a rack and cool for 10 minutes while you make the icing.

Step 6: Make the Silky Stovetop Fudge Icing

In a medium saucepan over medium heat, melt the butter with the cocoa and milk, whisking until smooth and just beginning to simmer at the edges, 30–60 seconds. Remove from heat. Whisk in the powdered sugar gradually until glossy and lump-free, followed by the vanilla and salt. For extra sheen and flow, whisk in the corn syrup (optional). If it thickens while standing, whisk in 1–2 teaspoons more milk to loosen.

Step 7: Pour and Set

Use a skewer to poke 10–12 small holes across the warm cake (optional, for an extra fudgy bite). Immediately pour the warm icing over the cake and nudge it to the edges with an offset spatula. If using, sprinkle toasted pecans or a pinch of flaky sea salt on top. Let the icing set for 15–20 minutes before slicing into 16 squares. Serve slightly warm or at room temperature.

Pro Tips

• Use hot coffee, not lukewarm. The heat helps bloom the cocoa for a deeper chocolate flavor.
• Room-temperature eggs and sour cream blend more easily and help the cake rise evenly.
• Prefer less sweetness? Reduce powdered sugar in the icing to 2 3/4 cups (330 g) and add a teaspoon of milk if needed.
• Line the pan with parchment for clean slices and easy removal, especially if transporting.
• For the glossiest icing, sift powdered sugar and keep the icing warm and pourable.

Variations

• Mocha Twist: Add 1 teaspoon espresso powder to the dry ingredients and use coffee in the icing instead of some of the milk.
• Texas Sheet Cake Vibes: Whisk 1 teaspoon ground cinnamon into the dry ingredients; top with toasted pecans.
• Gluten-Free: Use a reputable 1:1 gluten-free baking flour blend in place of all-purpose flour; mix gently and allow the batter to rest 5 minutes before baking.

Storage & Make-Ahead

Store the frosted cake tightly covered at room temperature for up to 3 days, or refrigerate for up to 5 days. For longer storage, cut into squares, wrap individually, and freeze up to 2 months; thaw at room temperature. The icing can be made a few hours ahead; rewarm gently over low heat, whisking in a splash of milk to restore a pourable texture. The cake is excellent baked the day before—ice it just before serving for a fresh glossy finish, or ice it warm and let set as directed.

Nutrition (per serving)

Approximate per 1 of 16 pieces: 400 calories; 16 g fat; 57 g carbohydrates; 4 g protein; 2 g fiber; 270 mg sodium.