Makes 12 Total Time 45 minutes +cooling
3/4 cup unsweetened cocoa powder, plus more for pan
1-1/2 cups all-purpose flour (spooned and leveled)
1-1/2 cups granulated sugar
1-1/2 teaspoons baking soda
3/4 teaspoon baking powder
3/4 teaspoon fine salt
2 large eggs
3/4 cup buttermilk
3 tablespoons vegetable oil
6 tablespoons unsalted butter, room temp
1/2 cup creamy peanut butter
1-1/2 cups marshmallow topping
confectioners’ sugar, for dusting
1 Preheat oven to 350 degrees F. Lightly coat 12 standard muffin cups with cooking spray, then dust with cocoa, tapping out excess. In a large bowl, whisk together cocoa, flour, granulated sugar, baking soda, baking powder, and salt. Using a mixer, beat in eggs, buttermilk, oil, and 3/4 cup water on medium until smooth, about 3 minutes.
2 Divide batter among cups and bake until a toothpick inserted in center of a cake comes out clean, about 20 minutes. Let cool in a pan on a wire rack 5 minutes, then remove cupcakes and let cool completely on rack.
3 In a large bowl, using mixer fitted with the paddle attachment, beat butter and peanut butter on high until fluffy, 3 minutes; fold in marshmallow topping. Transfer to a zip-top bag and cut off one corner to make a 1/2-inch opening.
4 With a melon baller, scoop out center of each cupcake base and set aside (these pieces will plug cupcakes after filling). Hollow out each cupcake a bit more, discarding crumbs. Fill cavities with peanut butter mixture and replace plugs. (Refrigerate in an air tight container, up to 1 week.) To serve, dust with confectioners’ sugar.