Preheat oven to 325°F and line cupcake tins with liners. Stir the espresso powder into the brewed espresso and let cool. Meanwhile whisk together flour and cocoa. In a separate bowl cream butter, then add brown sugar and eggs, beating until light and fluffy, scraping down sides of bowl as needed. Add vanilla, baking soda and salt, mixing thoroughly.

On low speed, stir in the flour mixture in 3 batches, alternating with 2 additions of sour cream, stirring until just combined. Add espresso mixture and beat until smooth.

Fill cupcake pans ¾ full. Bake for about 20 minutes, or until a toothpick inserted in center of cupcakes comes out nearly clean. Transfer to a wire rack and cool completely in pans before frosting.

In a heat-proof bowl over a pot of simmering water, whisk the egg whites, sugar and salt constantly until sugar is dissolved and temperature reads 140°F. Remove from heat. Beat with whisk attachment until stiff peaks form, about 7 minutes.

Add the butter, one pat at a time, beating on medium speed until all the butter is incorporated. Slowly add the vanilla and caramel sauce, beat until smooth and creamy.

Transfer to a pastry bag and pipe cupcakes with desired design. Garnish with caramel sauce and espresso beans.