Easy Rainbow Cupcakes with Vanilla Frosting – Sugar Geek Show

Ingredients

• 1 box white cake mix (I like Duncan Hines)
• 1 cup all purpose flour
• 1 cup granulated sugar
• 1/4 teaspoon salt
• 1 cup sour cream (room temperature)
• 1/2 cup unsalted butter (melted)
• 1 cup milk (room temperature)
• 3 large eggs (room temperature)
• 6 bottles gel food coloring: red, orange, yellow, green, blue, purple (2-3 tsps of each color)
• 6 ounces pasteurized egg whites ((from a box))
• 24 ounces powdered sugar
• 1 Tablespoon vanilla extract
• 1/2 teaspoon salt
• 24 ounces unsalted butter (softened)