I've made them a few times now but I think my favorite way to make them is as mini cupcakes, kind of like a shot of espresso, but a million times better :)

Mocha Brownie Cupcakes
makes about 22 full-sized cupcakes
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Ingredients:
for the cupcakes
11 Tablespoons unsalted butter, at room temperature
3 oz. unsweetened chocolate, finely chopped
1½ cups all-purpose flour
2 teaspoons espresso powder
½ teaspoon baking powder
½ teaspoon salt
3 large eggs
2 cups sugar
½ cup coffee liqueur
for the frosting
16 Tablespoons unsalted butter, at room temperature
3 cups confectioners' sugar, sifted
1 Tablespoon instant coffee granules
2 teaspoons hot coffee
1 teaspoon vanilla extract
Directions:
To make the cupcakes
Preheat the oven to 350°. Prepare 2 cupcake pans with paper liners and set aside. Place a heat-proof bowl over a pot of simmering water and in the bowl melt together the butter and chocolate, stirring until smooth. Remove the bowl from the heat and let cool.
While the chocolate mixture is cooling combine flour, espresso powder, baking powder and salt together in a medium bowl and set aside.
In the bowl of an electric mixer, beat together the egg and sugar until light and fluffy. Add in the coffee liqueur and chocolate mixer and beat until combined.
Gradually pour the flour mixture into the electric mixer bowl and beat until just combined.
Spoon the batter evenly between the cupcake liners, filling the cups about 2/3rds of the way.
Bake for 20-22 minutes, or until a toothpick inserted into the center of one of the cupcakes comes out clean. Cool the cupcakes in the pan for 5 minutes, then transfer to a wire cooling rack and cool completely.
To make the frosting
In the bowl of an electric mixer beat the butter at medium high speed until it is smooth. Slowly add in the confectioners' sugar until just blended, then increase mixer speed and beat until light and fluffy. Add in the coffee, coffee granules and vanilla extract and beat until well-blended.
Pipe the frosting onto the cooled cupcakes.
Source: Annie's Eats