Mini Vanilla Bean Cupcakes with Vanilla Buttercream Frosting

• 1 ¼ cups all-purpose flour
• 1 cup cake flour
• 1 teaspoon baking powder
• ½ teaspoon baking soda
• ½ teaspoon kosher salt
• 1 cup sour cream
• ½ cup milk
• 4 large egg whites at room temperature
• ½ cup unsalted butter at room temperature
• 1 ⅓ cups sugar
• 1 vanilla bean seeds scraped
• 2 teaspoons vanilla extract

For the vanilla buttercream frosting

• 1 cup unsalted butter softened and cut into cubes
• 4 cups confectioners’ sugar
• 1 tablespoon heavy cream
• 2 teaspoons pure vanilla extract
• ⅛ teaspoon salt
• Sparkling Sugar for garnish