1. Preheat oven to 365 degrees Fahrenheit. Line two cupcake pans with 12 cupcake liners.
2. In the bowl of an electric mixer, beat egg whites on high speed until stiff peaks form. Slowly add sugar, baking powder, potato starch, oil, and yolks. Mix until incorporated. Fold in blueberries.
3. Spoon batter into cupcake holders. Bake for 25 minutes or until tester comes out clean. Remove from oven and cool in baking tins for 5-10 minutes before removing to a wire rack.
4. To prepare crumb topping, raise oven temperature to 400 degrees Fahrenheit. Mix ingredients into a crumble. Bake for 10-15 minutes. Brush the muffins with oil (or spray with cooking spray) and sprinkle with the crumble.