Guinness Chocolate Cupcakes with Mocha Guinness Buttercream

Adapted from my these moist Guinness chocolate cupcakes are made with reduced Guinness beer for deep flavor. Theyre flecked with real espresso powder and topped with ultra creamy and flavorful mocha Guinness buttercream. Consider these your perfect St. Patricks Day dessert!
Ingredients
one 12ounce 355ml bottle Guinness beer
1 cup 125g allpurpose flour 
12 cup 41g unsweetened natural cocoa powder
1 and 12 teaspoons espresso powder
34 teaspoon baking soda
14 teaspoon salt

12 cup 1 Tablespoon 135ml vegetable or canola oil
1 cup 200g packed light or dark brown sugar
2 large eggs at room temperature
34 cup 180g fullfat sour cream at room temperature
2 teaspoons pure vanilla extract
Mocha Guinness Buttercream
2 Tablespoons reduced Guinness from step 1
2 teaspoons espresso powder
4 and 12 cups 550g confectioners sugar
1 Tablespoon 5g unsweetened natural cocoa powder
1 Tablespoon 15ml milk
1 teaspoon pure vanilla extract
pinch of salt to taste
Instructions
In a small saucepan bring the Guinness to a boil over mediumhigh heat. Once boiling reduce to medium heat and allow to simmer until reduced down to 23 cup about 20 minutes. Set 12 cup aside to cool for 1015 minutes before using in the cupcake batter. While its warm mix the rest of the reduced Guinness about 22 5 Tablespoons with the 2 teaspoons of espresso powder used in the frosting. Set this mixture aside for step 5. You can do this step 1 day ahead of time if needed. Refrigerate overnight. Bring reduced beer to room temperature before using in both the cupcake batter and frosting.
Preheat the oven to 350F 177C. Line a with cupcake liners. Line a second pan with 4 linersthis recipe makes about 16 cupcakes. Set aside
Whisk the flour cocoa powder espresso powder baking soda and salt together in a large bowl until thoroughly combined. Set aside. In a medium bowl whisk the oil brown sugar eggs sour cream and vanilla together until completely smooth. Pour the wet ingredients