1/2 cup Dutch-processed cocoa powder
1 cup boiling hot water
1 1/3 cups all purpose flour
2 teaspoons baking powder
1/4 teaspoon salt
1/2 cup unsalted butter, room temperature
1 cup granulated white sugar
2 teaspoons pure vanilla extract
Preheat oven to 375 degrees F . Lightly butter, or line 15 muffin cups with paper liners.
In a small bowl stir until smooth the boiling hot water and the cocoa powder. Let cool to room temperature.
Then in the bowl of your electric mixer, or with a hand mixer, beat the butter and sugar until light and fluffy. Add the eggs, one at a time, beating until smooth. Scrape down the sides of the bowl as needed. Beat in the vanilla extract. Add the flour mixture and beat only until incorporated. Then add the cooled cocoa mixture and stir until smooth. Fill pan about 2/3 full. Bake for 11 minutes, remove from oven, insert Reese's mini peanut butter cup into each cupcake and return to oven for exactly 6 more minutes. Test with toothpick, from the side when comes out clean they are done.
Chocolate Fudge Frosting:
4 ounces unsweetened chocolate, coarsely chopped
2/3 cup unsalted butter, room temperature
1 1/3 cups confectioners (powdered or icing) sugar, sifted
1 1/2 teaspoons pure vanilla
Melt the chocolate in a heatproof bowl placed over a saucepan of simmering water. Remove from heat and let cool to room temperature.
In the bowl of your electric mixer, or with a hand mixer, beat the butter until smooth and creamy (about 1 minute). Add the sugar and beat until it is light and fluffy (about 2 minutes). Beat in the vanilla extract. Add the chocolate and beat on low speed until incorporated. Increase the speed to medium-high and beat until frosting is smooth and glossy (about 2 -3 minutes)