Protein Pinata Cakes – Protein Milkshake

Ingredients

• 1 and 3/4 cups cake flour
• 1/2 scoop Protein Milkshake Cupcake Batter
• 3/4 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1/4 teaspoon salt
• 1/2 cup unsalted butter, softened to room temperature
• 1 cup granulated sugar
• 3 large egg whites, at room temperature
• 2 teaspoons pure vanilla extract
• 1/2 cup full-fat sour cream at room temperature
• 1/2 cup whole milk at room temperature
• 1/2 cup rainbow sprinkles, for filling
• 1 cup unsalted butter, softened to room temperature
• 4 - 5 cups confectioners' sugar
• 1/4 cup heavy cream or whole milk
• salt, to taste