Instructions

• Preheat oven to 350°F. Line a muffin tin with paper liners.
• Melt 1/2 cup unsalted butter in the microwave in short bursts or on the stovetop; let it cool slightly.
• In a medium bowl sift or whisk together 1 1/8 cups all-purpose flour, 1/4 cup unsweetened cocoa powder, 1 1/4 teaspoons baking soda, and 1/2 teaspoon salt.
• In a large bowl whisk 1 large egg and 3/4 cup granulated sugar until smooth. Whisk in the melted butter and 2 teaspoons vanilla extract until combined.
• Add the dry ingredients to the wet mixture and stir with a large spoon until the batter is smooth.
• Gradually whisk in 3/4 cup Kahlua until incorporated and the batter is uniform.
• Reserve a small handful of the chopped dark chocolate and/or white chocolate chips if you want to use them for garnish. Fold the remaining 4 ounces coarsely chopped dark chocolate and 1/2 cup white chocolate chips into the batter.
• Using a heaping 1/4-cup measure (or similar scoop), fill each prepared cupcake liner about 3/4 full.
• Bake for 15–18 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Remove from oven and let cupcakes sit in the pan for about 5 minutes, then transfer to a wire rack to cool completely before frosting.
• For the frosting: in the bowl of an electric mixer beat 1 cup (2 sticks) sweet cream butter on medium speed until smooth and creamy, about 2 minutes.
• With the mixer on low, add 3 1/2 cups powdered sugar gradually (about 1/2 cup at a time) until incorporated, then increase the speed to combine fully.
• Add 1 tablespoon Kahlua and 1 teaspoon vanilla extract, then beat on medium-high for 3–4 minutes, scraping down the sides of the bowl occasionally, until the frosting is pale and fluffy.
• Frost the cooled cupcakes with the Kahlua buttercream. If you reserved a small handful of chocolate or chips, use them to garnish the tops.