Preheat oven to 180C. Line two large baking trays with non stick paper.
Beat butter and brown sugar with an electric mixer until well combined and smooth. Add egg and vanilla. Beat until thoroughly combined. Add remaining ingredients and mix until well incorporated and dough comes together.
Divide mixture into 36 portions. Roll each portion into a ball and arrange on baking trays allowing room for spreading.
Bake in preheated oven for 15-18 minutes for a chewy cookie or 20-25 minutes for more crunch.