Preheat the oven to 350°F. Grease 12 individual 1-cup Bundt pans with 2 tablespoons of the butter.
Into a small mixing bowl, sift the flour, baking powder, baking soda, and salt together. Set aside.
In a large mixing bowl, cream together the remaining butter and the granulated sugar using an electric mixer fitted with the paddle attachment set on medium speed. Add the eggs one at a time, beating well after each addition. Add the melted chocolate and vanilla and beat to mix. Add the flour mixture 1/2 cup at a time, alternating with the milk, beating until everything is incorporated.
Fill each tin with 1/4 cup of the batter. Place some of the peanut butter chips in the center of the batter in each cup, then pour in the remaining batter to fill the tins. Bake until the cakes set, 18 to 20 minutes. Remove from the oven and let cool in the pans for 5 minutes, on wire racks, then flip out of the tins and cool for 5 minutes more.
In a small mixing bowl, combine the cocoa powder, confectioners’ sugar, and as much of the remaining milk as needed to whisk into a smooth glaze. Set the cakes on a wire rack and spoon equal amounts of the glaze over them. Allow the glaze to set before serving.
Yield: 12 individual cakes