- ½ cup buttermilk
- 4 large eggs
- 2 tsp. vanilla extract
- 2¼ cups all-purpose flour
- 1½ cups granulated sugar
- 1½ tsp. baking powder
- ½ tsp. baking soda
- ¾ tsp. salt
- 16 Tbsp. (2 sticks) butter, softened and cut into pieces
- 12 Tbsp. (1½ sticks) butter, softened and cut into pieces
- 2 cups brown sugar, packed
- ½ tsp. table salt
- ½ cup heavy cream
- 1 tsp. vanilla extract
- 2½ cups confectioners’ sugar, sifted
Make the cupcakes: Adjust the oven rack to middle position and preheat the oven to 350 degrees F. Fill cupcake pans with liners and set aside.
Whisk buttermilk, eggs, and vanilla in a large measuring cup. With mixer on low speed, mix flour, granulated sugar, baking powder, salt, and baking soda until combined. Bet in butter, one piece at a time, until only pea-sized pieces remain. Pour in half of buttermilk mixture and beat on medium-high speed until light and fluffy, about 1 minute. Slowly add remaining buttermilk mixture to bowl and beat until incorporated, about 15 seconds.
Scoop equal amounts of batter unto prepared pans and bake until golden and toothpick inserted in center comes out clean, 15 to 20 minutes. Cool cupcakes in pans for 10 minutes, then completely on wire racks (or in refrigerator for quicker cooling).
Make the frosting: Heat 8 tablespoons butter, brown sugar, and salt in a large saucepan over medium heat until small bubbles appear on perimeter of pan 4 to 8 minutes. Whisk in cream and cook until ring of bubbles reappears, about 1 minute. Take off heat and whisk in vanilla.
Transfer hot frosting to mixer bowl and gradually mix confectioners’ sugar in on low speed until incorporated. Increase speed to medium and beat until frosting is pale brown and just warm, about 5 minutes. Add remaining butter, 1 piece at a time, and beat until light and fluffy, about 2 minutes.
Spread or pipe frosting on top of cupcakes and serve.