Preheat oven to 350 degrees F (180 C). Line cupcake pans with paper liners and set aside.
Melt butter and set aside to cool slightly.
Using an electric mixer, beat eggs and sour cream or creme fraiche together at medium-high speed until well-combined. Add beer and vanilla, and mix again until mixture is even.
Combine cocoa powder, sugar, flour, baking soda, and cinnamon in a separate bowl. Whisk or stir briefly with a fork to blend.
Slowly add the dry ingredients into the wet batter, mixing continuously to blend. After all the dry ingredients are incorporated, add the melted butter and mix again until batter is evenly combined.
Pour batter into cupcake liners, filling each about 3/4 full. Bake for 20-25 minutes, until a toothpick inserted into the center comes out clean. Allow pans to cool on wire racks for about 10 minutes, then remove cupcakes and let cool completely.
To make the frosting, using an electric mixer, cream together the butter and cream cheese. Gradually add the powdered sugar, mixing until light and fluffy, then add the salt and vanilla. Beat well to combine, then add Irish cream, and beat again until frosting is a smooth consistency for piping. Frost cupcakes as desired.