Preheat oven to 350°F. Line a cupcake pan with 8 paper liners. 

In a large bowl or stand mixer, cream together butter and sugar. With mixer running on low, add egg whites, vanilla, salt and baking powder. Scrape bowl as needed. Alternate additions of flour and yogurt until fully combined and no streaks remain. Stir in sprinkles by hand.

Divide batter between prepared liners using a large cookie scoop. 

Bake for 18-20 minutes or until a toothpick inserted comes out clean. Cool in pan until easy to handle, then transfer to a wire rack to cool completely. 

In a large bowl or stand mixer, beat together butter and shortening. Add vanilla and powdered sugar, followed by heavy cream. Mix until light and fluffy and fully combined. Transfer frosting to a large piping bag fit with a desired piping tip. Pipe frosting onto cooled cupcakes. Immediately decorate with sprinkles. 

Serve immediately or store in an airtight container for up to several days. Cupcakes may also be stored in the refrigerator.