In the bowl of a stand mixer using the paddle attachment (or in a large bowl using a handheld electric mixer), beat butter on medium-high speed until smooth.
1 cup unsalted butter,
Add vanilla and salt and beat on medium-high speed until blended.
2 teaspoons vanilla extract, 1 pinch fine sea salt
Add cocoa powder and beat well on medium speed. Scrape the bowl.
½ cup black cocoa
Add sugar slowly – one cup at a time – beating well on medium speed and scraping the bowl often. When all sugar is added the frosting will be slightly dry.
3 ½ cups confectioners' sugar
Add milk and beat on high speed until the frosting is light and fluffy.
2 Tablespoons whole milk
Place a damp towel or paper towel over the bowl of frosting and set aside for 2 hours to let the color deepen while you bake the cupcakes.
Make the cupcake batter.
Preheat oven to 350º F. Line a cupcake pan with paper liners and set aside.
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
1 ⅛ cup all-purpose flour, 1 cup granulated sugar, ⅜ cup black cocoa powder, 1 teaspoon baking powder, ¾ teaspoon baking soda, ½ teaspoon fine sea salt
To the dry ingredients add milk, oil, sour cream, egg, and vanilla. Stir until well combined. The batter will be thick, similar to the texture of brownie batter.
3 ounces whole milk, ¼ cup vegetable oil, 2 Tablespoons full-fat sour cream, 1 large egg,, 1 teaspoon vanilla extract
Add hot coffee to the batter, carefully mixing with a whisk until well blended. The batter will now be very thin.
4 ounces hot coffee
Bake the cupcakes.
Pour the batter into the cupcake liners, filling each ⅔ full.
Bake the cupcakes for 18-20 minutes, or until the tops sprigs back when gently poked and a cake tester inserted into the center of a cupcake comes out clean or with just a few moist crumbs.
Let the cupcakes cool completely before frosting.
Frost the Cupcakes
Using a piping bag fitted with a piping tip or an offset spatula, pipe or spread frosting onto the cupcakes. Top with sprinkles, if using.
Notes
Storage: These cupcakes can be stored in an airtight container at room temperature for up to 4 days.Freezing: Wrap completely cooled cupcakes with plastic wrap before sealing in a plastic bag or airtight container and freezing. Cupcakes can be wrapped together in groups and do not need to be individually wrapped. Defrost cupcakes at room temperature before frosting and serving.