Preheat oven to 350 degrees. In a medium bowl, mix together the flour, baking soda, baking powder and salt. Mix to combine and set aside.
In a microwave safe bowl, melt the butter. In a large bowl, place the sugar and mix with the melted butter. Whisk in the egg whites, sour cream, milk and vanilla. Gradually mix in the dry ingredients a little at a time and whisk together until there are no lumps.
Pour mixture into cupcake lined tin 2/3 of the way full. Bake for 20 minutes or until a toothpick inserted comes out clean. Place tin on wired rack for 5 minutes to cool. Take out cupcakes and cool completely on wired rack.
Rice Krispies Treats Frosting:
In the bowl of an electric mixer, place the sugar, egg whites, water and cream of tartar. Whisk on medium speed until foamy.
Over a double boiler, whisk mixture until sugar is dissolved, about 5-7 minutes.
Place back on the mixer and whisk on high speed until stiff peaks form. About 15 minutes, they will be bright white and glossy. Add in the vanilla, mix to combine. Fold in the rice krispies cereal.
Top cupcakes with frosting and garnish with the Rice Krispies Treats, serve and enjoy!