Chocolate peanut butter cake

Makes two 9-inch (23cm) layers. Rounded quantities below are for the whole cake.

Adapted from Preppy Kitchen’s recipe. Flat-layer guide.

All amounts are by weight, including liquids. Baker’s percentages use the cake’s 280g flour as 100% throughout, including frosting and ganache; they are not shares of the total mixture. For example, 50% means 140g.

Cake

• 280g [100%] all-purpose flour
• 460g [164.3%] sugar
• 85g [30.4%] unsweetened cocoa
• 200g [71.4%] buttermilk
• 130g [46.4%] beaten egg (beat 3 large eggs; weigh without shells)
• 140g [50%] vegetable oil
• 10g [3.6%] vanilla
• 8g [2.9%] baking soda
• 5g [1.8%] baking powder
• 4g [1.4%] fine salt
• 200g [71.4%] hot coffee or water

Frosting

• 290g [103.6%] softened unsalted butter
• 275g [98.2%] creamy, no-stir peanut butter
• 500g [178.6%] powdered sugar
• 10g [3.6%] vanilla
• 1g [0.4%] fine salt
• 50–60g [17.9–21.4%] milk

Ganache

• 145g [51.8%] chopped dark chocolate
• 100g [35.7%] heavy cream

Method

1. Grease two 9-inch round cake pans, at least 2 inches deep; line bottoms with parchment. Heat oven to 350°F (175°C). Fill no more than ⅔ full; bake any extra batter separately.
2. For flatter layers, soak fabric cake strips 5–10 minutes, squeeze, and fit around pans.
3. Sift cocoa, then whisk in the other dry cake ingredients. In another bowl, whisk room-temperature buttermilk, eggs, oil, and vanilla. Stir wet into dry; the batter will be thick. Add hot coffee or water and whisk just until smooth.
4. Divide evenly. Start checking at 30 minutes; bake until centers spring back and a tester has no wet batter. Timing may vary with your pan and cake strips. Cool 15 minutes; unmold and cool completely.
5. Start the frosting: Use softened butter that dents when pressed but is not melted. With a stand mixer’s paddle or a hand mixer, beat butter and peanut butter on medium-high for 2–3 minutes, until fluffy and free of butter lumps. Scrape the bowl; briefly mix in vanilla and salt.
6. Add sugar: On low speed, gradually add 250g powdered sugar. Scrape the bowl, mix in 50g milk, then slowly add the remaining 250g sugar.
7. Finish the frosting: Beat on medium for about 2 minutes. It should spread easily and hold soft ridges. If stiff or grainy, beat in extra milk 5g at a time, up to 10g total.
8. Once both layers are completely cool, spread frosting over the first, add the second, then cover the top and sides. Refrigerate 20 minutes to firm the frosting.
9. Heat cream until steaming, without boiling. Pour over chopped chocolate; leave 5 minutes, then stir until glossy. Cool about 15 minutes, stirring occasionally, until barely warm. Spread over the chilled cake; refrigerate 30 minutes before slicing.

Only one pan? Make two separate half-batches of the cake batter, mixing the second just before baking. Cool, clean, and re-line the pan between layers. Use half of every cake ingredient per batch, including 65g beaten egg. Make the frosting and ganache once using the full amounts above.