Before you start
Peanut butter frosting is the best frosting that hardly anyone makes: peanut butter whipped with butter and icing sugar into something between mousse and fudge. It wants the darkest chocolate sponge you can give it, which is the same buttermilk cocoa batter the site uses everywhere, because it works. A peanut butter cup on top announces the contents.
Everything you need
- 1 cup (125 g) all-purpose flour
- ⅓ cup (28 g) cocoa powder
- ¾ cup (169 g) caster sugar
- ¾ tsp baking soda
- ½ tsp fine salt
- 1 egg
- ¾ cup (184 g) buttermilk
- ⅓ cup (73 g) vegetable oil
- 1 tsp vanilla extract
- ¾ cup (194 g) smooth peanut butter (for the frosting)
- ½ cup (113 g) unsalted butter, soft (for the frosting)
- 1½ cups (180 g) powdered sugar, sifted (for the frosting)
- 2 tbsp (29 g) heavy cream (for the frosting)
- 12 mini peanut butter cups, to top
Weigh, don't scoop. Measuring flour by cups can overpack it and dry out your bake. Tap any ingredient to open its converter.
Method
-
Heat the oven to 175°C / 350°F. Line a 12 hole tin. Whisk the flour, cocoa, sugar, baking soda and salt.
For this step
- 1 cup (125 g) all-purpose flour
- ⅓ cup (28 g) cocoa powder
- ¾ cup (169 g) caster sugar
- ¾ tsp baking soda
- ½ tsp fine salt
- 1½ cups (180 g) powdered sugar
-
Whisk the egg, buttermilk, oil and vanilla, combine with the dry mix until just smooth, and divide between the cases.
For this step
- ¾ cup (184 g) buttermilk
- 1 tsp vanilla extract
- ¾ cup (194 g) smooth peanut butter (for the frosting)
- ½ cup (113 g) unsalted butter
- 12 mini peanut butter cups
-
Bake 17 to 19 minutes until springy. Cool completely.
-
Beat the peanut butter and butter together for 3 minutes until fluffy and lightened.
For this step
- ¾ cup (194 g) smooth peanut butter (for the frosting)
- ½ cup (113 g) unsalted butter
- 12 mini peanut butter cups
-
Add the powdered sugar in two stages, then the cream, and beat 2 more minutes until it holds soft peaks like a mousse.
For this step
- ⅓ cup (28 g) cocoa powder
- ¾ cup (169 g) caster sugar
- 1½ cups (180 g) powdered sugar
- 2 tbsp (29 g) heavy cream (for the frosting)
-
Pipe high swirls onto the cooled cupcakes and press a peanut butter cup into each. A flurry of chocolate shavings if you're feeling editorial.
For this step
- ¾ cup (194 g) smooth peanut butter (for the frosting)
- ½ cup (113 g) unsalted butter
- 12 mini peanut butter cups
Baker's tips
- Standard smooth commercial peanut butter, not the natural drippy kind. Natural peanut butter splits this frosting into oil and sadness.
- The frosting stiffens as it stands. If it gets hard to pipe, 10 seconds of rebeating brings it back.
Make it your own
- Core each sponge and hide a teaspoon of raspberry jam inside, the PBJ move.
- A drizzle of melted dark chocolate over the swirls sets into a shell.
Storing & freezing
Lidded at room temperature for 2 days, fridge for 4. The frosting freezes for a month on its own and rewhips well.
Frequently asked
Can I use natural peanut butter for frosting?
Better not to. Natural peanut butter separates and makes greasy, split frosting. The stabilised supermarket kind whips into a stable mousse every time.
Why is my peanut butter frosting stiff?
Peanut butter sets firm as it sits and cold thickens it further. Beat in an extra spoonful of cream, or rebeat briefly at room temperature to loosen.
Baking in a different unit? Use the cups ↔ grams converter or the recipe scaler to halve or double this recipe.
More to bake
A note on cooking safely. Recipes are provided for informational purposes only and are not medical or nutritional advice. Cooking times, temperatures and quantities are suggestions: use your own judgement, and check that meat, poultry, fish and eggs are properly cooked before serving.
Consult a qualified healthcare professional before making dietary changes, particularly if you have allergies, a medical condition or specific nutritional requirements.