Preheat traditional waffle iron to medium. Meanwhile, stir flour, Rice Krispies, cornstarch, sugar, baking powder, baking soda, and salt together in large bowl. Whisk egg yolks, milk, vanilla, and oil together in medium bowl.
With electric mixer or balloon whisk, beat egg whites in bowl to soft peaks. Pour milk mixture over dry ingredients and whisk until combined. Whisk in beaten whites until just combined. Do not overmix; a few streaks of whites should be visible.
Pour 2/3 cup batter into center of preheated waffle iron and use back of dinner spoon to spread batter toward outer edges (batter should reach about 1/2 inch from edges of iron before closing lid). Make sure to fill the waffle iron as directed; if you don't use enough batter, the Rice Krispies can scorch.Close lid and cook until deep golden brown, 3 to 4 minutes. Serve immediately.
KEEPING THEM WARM: Waffles are best served right off the waffle iron, but they can be reheated so everyone can eat at once. Transfer the cooked waffles to a wire rack set on top of a baking sheet in a 400-degree oven and bake until crisp and hot, 3 to 5 minutes.
KEEPING THEM FROZEN: Waffles freeze beautifully. After cooling the waffles, wrap each in plastic, then freeze in a zipper-lock bag for up to one month. To serve, place the waffles on a wire rack set on a baking sheet and bake in a 400-degree oven until crisp and hot, about 5 minutes.