Grease and flour (2) 9” cake pans. Line bottoms of the pans with parchment paper. Set pans aside. (Note: Make sure the pans are at least 2” deep.)
Using a large saucepan, add beer and butter; place over medium heat until butter has fully melted and mixture just begins to simmer.
Remove pan from heat and whisk in the cocoa powder until mixture is smooth. Set pan aside to cool to room temperature.
Using a large bowl, sift together the flour, sugar, baking powder and salt; set bowl aside.
In a separate bowl, whisk together eggs, sour cream and vanilla extract. Transfer this mixture into the bowl of a countertop mixer.
Add the beer-cocoa mixture; stir on low speed until well combined.
Add the flour mixture; stir on low speed until well combined. (Tip: Don’t forget to scrape down the sides of the bowl.)
Pour batter evenly into the prepared pans.
Bake at 350°F for 35-38 minutes, or until a toothpick inserted into the center of the cakes comes out mostly clean.
Let cakes cool in pans for 10 minutes before transferring to a cooling rack until completely cool.
For the Coffee Buttercream
Using a countertop mixer, cream together the butter and confectioner’s sugar until light and fluffy.
Using a small bowl, whisk together the espresso powder and water. Add this mixture and the vanilla extract to the bowl; mix until well combined.
Place one cake layer on large platter. Spread ~¾ cup of frosting on top. Place 2nd layer of cake on top. Use remaining frosting on top and sides of cake.
{Optional} Garnish top of cake with chocolate sprinkles.