Preheat oven to 350 F. Line a muffin pan with paper cups. In a large mixing bowl, cream together butter and sugar until light and fluffy using a mixer (either hand-held or stand mixer).
Beat in the egg and vanilla. Add the peanut butter and beat until incorporated. In another bowl whisk together the flour, baking powder, baking soda and salt. Add the powder mixture to the mixing bowl and alternately add the milk. Add the powders in three additions and the milk in two additions.
Spoon the batter into 12 paper cups. bake for 2-25 minutes, or until a toothpick inserted at the center of a cupcake comes out clean. Let the cupcakes cool on a wire rack.
Combine butter and chopped chocolates in a heatproof bowl. In a small saucepan, heat the cream until it starts to bubble. Turn off heat and pour the hot cream over the chocolate and butter in the bowl. Stir until smooth.
Dip the top of the cupcakes in the chocolate, then sprinkle some chopped peanuts. Let the cupcakes sit for a moment until the chocolate is set.
Recipe adapted from Best Cakes and Cupcakes, Canadian Living, Spring/ Sumer 2013