8 tablespoons (1 stick) unsalted butter, cut into 4 pieces
2 ounces bittersweet chocolate, chopped
1/2 cup Dutch-processed cocoa powder
3/4 cup all-purpose flour
1/2 teaspoon baking soda
3/4 teaspoon baking powder
2 eggs
3/4 cup granulated sugar
1 teaspoon vanilla extract
1/2 teaspoon table salt
1/2 cup sour cream

Ingredients for Peanut Butter Frosting:

1 cup confectioners’ sugar
1 cup creamy peanut butter
5 tablespoons unsalted butter, at room temperature
3/4 teaspoon vanilla extract
1/4 teaspoon kosher salt
1/3 cup heavy cream
12 miniture reese’s peanut butter cups, halved