Preheat oven to 350F and grease a wide mug or ramekin (make sure it's oven-safe) with oil or butter and set aside.
Melt butter in a small bowl.
Mix in sugar, vanilla, and the egg yolk.
Next, stir in oat flour, baking soda, and salt. Your mixture will be a bit sticker than classic cookie dough (see pictures). Mix in a small handful of chocolate chips.
Spread batter evenly into mug or ramekin. Add more chocolate chips on top. Bake until the edges become slightly crispy, about 20-22 minutes.
Notes
*you can buy oat flour at the store or you can make your own. I personally always make my own because it is so easy and cheap! I have a tutorial on how to make oat flour in my Instagram highlights.**save your egg white for a scramble!