This chocolate birthday cake is a one-bowl recipe: two tender 8-inch layers made with cocoa, oil and hot coffee, covered in a fluffy chocolate buttercream with no raw eggs. It takes 15 minutes to mix and about 35 minutes to bake, and it stays moist for days.

Why You'll Love This Chocolate Celebration Cake

Everything goes into one bowl, and you only need a whisk or a hand mixer. No creaming butter and sugar.

Oil instead of butter keeps the crumb soft even straight from the fridge, because oil stays liquid when cold. The hot coffee wakes up the cocoa and makes the cake taste more chocolatey, not like coffee.

The frosting is a simple cocoa buttercream. It spreads easily, holds swirls well and cuts cleanly, so the slices look as good as the whole cake.

Ingredients

For the cake

• 250 g (2 cups) all-purpose flour, spooned and leveled
• 400 g (2 cups) granulated sugar
• 65 g (¾ cup) unsweetened cocoa powder
• 9 g (1½ tsp) baking soda
• 6 g (1½ tsp) baking powder
• 6 g (1 tsp) fine salt
• 2 large eggs, at room temperature
• 240 ml (1 cup) whole milk, at room temperature
• 120 ml (½ cup) vegetable or canola oil
• 10 ml (2 tsp) vanilla extract
• 240 ml (1 cup) hot water or hot brewed coffee

For the chocolate buttercream

• 340 g (1½ cups) unsalted butter, softened
• 65 g (¾ cup) unsweetened cocoa powder
• 480 g (4 cups) powdered sugar, sifted
• 80 ml (⅓ cup) heavy cream or whole milk, at room temperature, plus 1–2 tbsp if needed
• 10 ml (2 tsp) vanilla extract
• 1 g (¼ tsp) fine salt

How to Make Chocolate Birthday Cake

1. Heat the oven and prep the pans. Heat the oven to 350°F (175°C) with a rack in the center. Grease two 8-inch (20 cm) round cake pans, line the bottoms with circles of parchment paper, grease the parchment and dust the pans with a spoonful of cocoa powder, tapping out the excess.
2. Whisk the dry ingredients. In a large bowl, whisk the flour, sugar, cocoa powder, baking soda, baking powder and salt for about 30 seconds, pressing out any cocoa lumps against the side of the bowl.
3. Add the wet ingredients. Add the eggs, milk, oil and vanilla. Beat with a hand mixer on medium speed for 2 minutes, or whisk hard by hand, until the batter is smooth, glossy and thick.
4. Stir in the hot liquid. Pour in the hot water or coffee and stir on low speed until it's fully mixed in. The batter will be very thin, almost like chocolate milk. That's how it should look.
5. Bake. Divide the batter evenly between the pans (a kitchen scale makes this easy) and tap each pan on the counter to pop large bubbles. Bake for about 35 minutes, without opening the oven for the first 25. Start checking at 30 minutes. The layers are done when a toothpick in the center comes out with a few moist crumbs but no wet batter, and the tops spring back when pressed lightly.
6. Cool the layers. Cool the cakes in their pans on a wire rack for 10 minutes. Run a thin knife around the edges, turn the layers out, peel off the parchment and let them cool completely, about 1 hour. Warm cake will melt the frosting.
7. Make the frosting. Beat the butter on medium-high speed for 2 minutes until pale and creamy. Add the cocoa powder and powdered sugar and mix on low until no dry streaks remain. Add the cream, vanilla and salt, then beat on medium-high for 2 to 3 minutes until light and fluffy. If it's too stiff to spread, beat in 1 to 2 tablespoons more cream.
8. Fill the cake. If the layers domed, trim the tops flat with a serrated knife. Set one layer on a cake stand or plate and spread about 1 cup of frosting over it, right to the edge.
9. Crumb coat. Place the second layer on top, bottom side up, so the flat side faces up. Spread a very thin layer of frosting over the top and sides to trap loose crumbs, then chill the cake for 15 minutes until that layer feels firm.
10. Frost and finish. Spread the remaining frosting over the cake with an offset spatula or the back of a spoon, then press and lift to make swirls. Top with chocolate curls or fresh raspberries if you like. Cut with a long knife dipped in hot water and wiped dry between slices.

Tips for a Moist Chocolate Cake

• Measure the flour lightly. A dry, dense cake almost always comes from packed flour. Spoon it into the cup and level it off, or weigh it. King Arthur has a clear guide on how to measure flour if you're unsure.
• Don't overbake for a moist, tender crumb. Pull the layers when the toothpick still shows a few moist crumbs. A clean toothpick means the cake has gone a minute or two too far, and it will keep cooking from its own heat as it cools.

• Keep the oven door shut. Opening it in the first 25 minutes lets the heat drop before the structure sets, which is the main reason for a sunken middle.
• Fix grainy frosting. Sift the powdered sugar and use butter soft enough to press a finger into easily. If it still looks grainy, beat in another tablespoon of cream for a minute.
• Use a crumb coat. A thin first layer of frosting, chilled until firm, keeps dark crumbs out of the final coat. It's the easiest way to frost without crumbs.

Variations

Sheet cake

Bake the batter in a greased 9x13-inch (23x33 cm) pan at the same temperature for about 35 to 40 minutes, using the same toothpick test. Frost it right in the pan with about two-thirds of the buttercream.

Cupcakes

Fill lined muffin cups two-thirds full and bake for 18 to 22 minutes. The recipe makes about 24 cupcakes.

Raspberry filling

Spread a thin layer of raspberry jam over the bottom layer before the frosting. The tart fruit cuts through the sweetness.

What to Serve with It

Fresh raspberries or strawberries on the side are the simplest match, since their sharpness balances the rich frosting. A scoop of vanilla ice cream or a spoonful of lightly sweetened whipped cream works too.

Cold milk or coffee suits it well. If you're planning a birthday dinner, a main like herb-roasted chicken leaves room for a generous slice afterward.

Storage, Freezing and Reheating

Room temperature: Cover and keep the frosted cake at room temperature for up to 2 days. A cake dome or large upturned bowl works well.

Refrigerator: Refrigerate the cake for up to 5 days. Bring it to room temperature before serving, about 1 hour for slices. Cold buttercream tastes dull and the crumb feels firm.

Freezer: Freeze unfrosted layers wrapped in plastic wrap and foil for up to 3 months. Thaw them, still wrapped, at room temperature so condensation forms on the wrap, not the cake.

Reheating: The cake doesn't need reheating. A fridge-cold slice can take 10 seconds in the microwave, but no longer, or the frosting melts.

Frequently Asked Questions

Can I make chocolate birthday cake ahead of time?

Yes. Bake the layers, cool them completely, then wrap each one well and freeze unfrosted for up to 3 months. Thaw them, still wrapped, at room temperature before frosting. Once frosted, the cake keeps covered at room temperature for up to 2 days.

How do I know when the cake layers are done?

Start checking at 30 minutes. A toothpick in the center should come out with a few moist crumbs but no wet batter, and the top should spring back when pressed. Most ovens get there in about 35 minutes.

Why did my cake sink in the middle?

It was usually underbaked, or the oven door was opened before the structure set. Old or extra leavening can also make it rise fast and fall. Bake until the toothpick test passes and keep the door closed for the first 25 minutes.

Why is my chocolate frosting grainy?

Unsifted powdered sugar and cold butter are the usual causes. Sift the sugar, start with soft butter, and beat for the full 2 to 3 minutes. A tablespoon of cream beaten in at the end smooths it out.

How long does chocolate birthday cake keep?

Cover and keep the frosted cake at room temperature for up to 2 days, or refrigerate it for up to 5 days and bring it to room temperature before serving. Unfrosted layers, wrapped well, freeze for up to 3 months.

Bake the layers a day early, frost on the day, and the cake is ready when the candles are.