Chocolate Cupcakes and Peanut Butter Icing

INGREDIENTS

• 1/2 cup sour cream, at room temperature
• 2 extra-large eggs, at room temperature
• 12 tablespoons (1 1/2 sticks) unsalted butter, at room temperature
• 1 cup good cocoa powder
• 1 1/2 teaspoons baking soda
• 1 cup creamy peanut butter
• Chopped salted peanuts, to decorate, optional
• 3/4 teaspoon pure vanilla extract
• 1 3/4 cups all-purpose flour
• 1/3 cup heavy cream
• 1/2 teaspoon kosher salt
• 5 tablespoons unsalted butter, at room temperature
• 1 cup confectioners' sugar
• Kathleen's Peanut Butter Icing, recipe follows
• 2 teaspoons pure vanilla extract
• 2/3 cup granulated sugar
• 2/3 cup light brown sugar, packed
• 1/4 teaspoon kosher salt
• 2 tablespoons brewed coffee
• 1 cup buttermilk, shaken, at room temperature