In a large mixing bowl, combine cake mix, egg whites, BAILEYS® Creamer, vegetable oil, sour cream and vanilla extract. Beat on medium speed until all ingredients are well mixed. Scrape down the sides of the bowl and stir from the bottom.
Divide batter evenly between lined cupcake pan. Bake at 350° for 15-18 minutes. Check for doneness by inserting a toothpick into the center of the cupcake. If the toothpick comes out clean, your cupcake is done. Cool completely.
Beat butter in mixer on medium speed until smooth and creamy: 2-3 minutes.
In a small glass, combine one tablespoon of BAILEYS® Mudslide Coffee Creamer with one teaspoon of espresso powder. Stir until most of the powder is dissolved. Add creamer to butter and beat until well incorporated.
Slowly add powdered sugar 1 cup at a time while continuing to beat on medium speed. As the frosting begins to thicken, add one teaspoon of BAILEYS® Mudslide Coffee Creamer at a time to help smooth out frosting. Once powdered sugar is incorporated, beat for another minute or two until the frosting is light and fluffy. Frost cooled cupcakes.
Top with chocolate sprinkles or chocolate shavings.