1/2 cup Guinness
1/2 cup (1 stick) butter
1 (16-ounce) box Trader Joe’s Brownie Truffle Baking Mix
1 (8-ounce) container mascarpone
4 tablespoons butter, at room temperature
1 tablespoon brewed coffee (or 1 teaspoon instant coffee granules)
1-1/2 to 2 cups powdered sugar
Preheat oven to 350°F. Line a muffin tin with paper liners. In a medium saucepan, bring the Guinness and butter to a boil. Reduce heat and simmer until the butter is melted. Add baking mix and stir to combine. Crack the eggs into a small bowl and whisk to combine. Stir eggs into Guinness mixture. Fill paper liners 2/3 full. Bake until a toothpick inserted into the center of a cupcake comes out clean, about 25 minutes. Cool before frosting.
With an electric mixer, combine the mascarpone, butter, and coffee. Beat in 1-1/2 cups powdered sugar. Adjust sweetness to taste with additional powdered sugar, if desired. Frost the cooled cupcakes.
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