For the cupcakes:
- 1 cup (120g) cake flour
- 1 teaspoon baking powder
- 1/4 teaspoon salt
- 1/2 cup (100g) granulated sugar
- 1/4 cup (60g) unsalted butter, melted
- 1 large egg white
- 1 teaspoon vanilla extract
- 1/4 cup (60ml) whole milk
- 2 tablespoons (30g) sour cream
For the buttercream frosting:
- 1/2 cup (113g) unsalted butter, softened
- 2 cups (240g) powdered sugar
- 1 teaspoon vanilla extract
- 2 tablespoons (30ml) heavy cream