Preheat oven to 350F. Spray muffin tins with nonstick spray or line with paper liners.
Heat beer and butter in a large saucepan over medium heat until butter is melted. Remove from heat.
Whisk sugar and cocoa into beer mixture. If cocoa is lumpy, be sure to sift cocoa prior to adding to the beer mixture.
In a medium bowl, combine sour cream, eggs, vanilla extract, and chocolate extract. Combine sour cream mixture with beer mixture, whisking until smooth.
In a large bowl, combine dry ingredients (flour, baking powder, baking soda, and salt). Stir to combine. Pour beer mixture into dry ingredients and whisk until smooth. Divide between muffin tins, filling each about ¾ full. You will get about 30 cupcakes.
Bake 13-15 minutes, or until a toothpick inserted in the center comes out clean. I rotate my pans halfway through baking to ensure an even bake.
Cool in pans 10 minutes. Remove from pans and allow to cool completely on wire racks.
Buttercream:
Beat butter and espresso powder until smooth. Sift powdered sugar into mixer bowl, one cup at a time, mixing until smooth after each addition.
If buttercream is too stiff, add heavy cream or whole milk by the tablespoonful until you reach the desired consistency. If buttercream is too runny, add additional powdered sugar.
Top each cupcake with espresso buttercream. If you like, decorate with dark chocolate and chocolate-covered espresso beans.Enjoy!
Notes
Note on chocolate extract: I highly recommend this (sometimes overlooked) extract! It lends an amazing depth of flavor to chocolate baked goods! If you can't find it in your local grocery store, you can find some [here]. Even better, makes yourself some [Homemade Chocolate Extract] for next time!