Cream the butter with the brown sugar and white sugar until soft and fluffy. There should be no large piles of sugar in the bowl.
Add the vanilla extract and egg yolk to the bowl and beat well again until full incorporated
Pour the oat flour and baking soda into the bowl and gently fold into the batter with a rubber spatula. Be careful not to over mix this step and only mix until no flour clumps remain.
Sprinkle the mini chocolate chips over the batter and fold into the dough until distributed.
Scoop the dough onto a baking sheet lined with parchment paper. Leave at least 2 inches in between each cookie.