For the cupcakes:
1 1/4 cups all-purpose flour
1/2 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
6 tablespoons melted butter
1 cup granulated sugar
2 XL egg whites
2 teaspoon vanilla extract
1 1/8 cup plain nonfat yogurt
a handful of rainbow sprinkles (jimmies), optional

Cream Cheese Frosting
About 1/3 cup and 3 T of softened butter
10 oz cream cheese
3 cups powdered sugar
1 1/2 tsp vanilla extract