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

In a large bowl, cream together butter and sugar until light and fluffy. Mix in egg white and vanilla until smooth. While mixing on low, sprinkle in salt and baking powder. Continue mixing on low, add half of the flour, followed by half of the yogurt. Repeat with remaining flour and yogurt, mixing until batter is just combined and no streaks remain. 

Divide batter between prepared liners, using a large cookie scoop, or roughly filling 3/4 full. 

Bake for 18-20 minutes or until cupcakes are set. Cool in pan for several minutes, until easy to handle, then transfer to a wire rack to cool completely. 

In a large bowl, beat together butter, shortening and vanilla until smooth. Add powdered sugar in 1/2 cup batches, mixing well between additions. Continue mixing until fully combined and smooth. 

Frost fully cooled cupcakes with desired method. Immediately top off with sprinkles, if desired. 

Store in an airtight container or chill overnight, bringing to room temperature prior to serving.