Heavenly Vanilla Cupcakes

Ingredients

• 1 tsp vanilla extract
• 3 egg whites
• 1 cup granulated sugar
• 1/2 cup sour cream
• 1 tbsp vanilla extract
• 1 tbsp heavy cream
• 4 cups confectioners' sugar
• 1/4 tsp baking soda
• 1 pinch kosher salt
• 1/4 tsp kosher salt
• 1 1/2 tsp baking powder
• 1 cup unsalted butter, room temperature
• 3/4 cup unsalted butter, room temperature
• 1 2/3 cups all-purpose flour
• 1/2 cup whole milk
• 1 tbsp whole milk