In a bowl, whisk the egg whites until they are very frothy.

In a separate bowl, mix the two flours and baking powder, and then with a knife or fork, cut in the cold butter (or coconut oil) and add salt if using. You want to make a crumbly mixture.

Let this sit in the refrigerator for 15–20 minutes.

Preheat oven to 400°F (205°C).

Remove flour/butter mixture from refrigerator, and gently fold in the egg whites, stirring to combine.

Bake for 12–15 minutes or until golden brown.