12 tablespoons (1 ½ sticks) unsalted butter, at room temperature
2/3 cup granulated sugar
2/3 cup light brown sugar, packed
2 extra-large eggs at room temperature
2 teaspoons pure vanilla extract
1 cup buttermilk, shaken, at room temperature
½ cup sour cream, at room temperature
2 tablespoons brewed coffee
1 ¾ cups all-purpose flour
1 cup good cocoa powder
1 ½ teaspoons baking soda
½ teaspoon kosher salt
Miniature Reese’s Peanut Butter Cups, to decorate (optional)
Kathleen’s Peanut Butter Icing
1 cup confectioners’ sugar
1 cup creamy peanut butter
5 tablespoons unsalted butter, at room temperature
¾ teaspoon pure vanilla extract
¼ teaspoon kosher salt
1/3 cup heavy cream