Preheat oven to 360 degrees F (182 degrees C).
Combine flour, brown sugar, baking powder, and salt in a mixing bowl.
Add oats to a food processor and pulse until finely milled.
Combine oats with other dry ingredients.
Add melted butter and splash of vanilla - gently combine until you have one cohesive dough.
Roll out dough on a well floured surface to about 5mm thick. Warning - the dough is crumbly, so you may have to add a decent amount of flour to the top to stop it from sticking to the rolling pin.
Cut out circles using a cookie cutter or a glass - when done, you can re-roll out the leftover dough (the more you do this, the crumblier it will be, so just know it may be difficult!).
Transfer cookies to a baking tray lined with parchment paper. Use a fork to gently prick the top of each cookie.
Bake for 15-20 minutes or until you see lightly golden edges and the bottoms are golden brown.
Let cool on a baking rack; if you want to, you can dip the cookies in melted chocolate, but this is totally optional! Let the cookies with chocolate set in the fridge (or at room temperature if you're using tempered chocolate) and enjoy!