Key Lime Cupcakes - Cupcake Fanatic

Ingredients

• 1 1/2 cups all-purpose flour, sifted
• 1 tsp. baking powder
• 1/4 tsp. coarse salt
• 1/2 cup whole milk, room temperature
• 1 tsp. pure vanilla extract
• 2 tbsp key lime juice
• 1 tbsp key lime zest
• 1/2 cup (1 stick) unsalted butter, room temperature
• 1 cup sugar
• 1 large egg, room temperature
• 2 large egg whites, room temperature
• 1 cup (2 sticks) unsalted butter , firm but not cold
• 1/8 tsp. salt
• 3 1/2 cups confectioners’ sugar, sifted
• 1/2 tsp vanilla extract
• 1 tsp. key lime juice
• 1/2 tsp. milk (only if necessary)