20 pieces

unsalted butter 90g
black sugar 30g
sugar 30g
egg 1
plain flour 140g
baking powder 1/2 tsp
baking soda 1/4 tsp
oatmeal 30g
72% chocolate 50g

steps for mixture in order:

unsaltd butter > black sugar + sugar > egg > flour + baking soda + baking powder > oatmeal > chocolate

180 degree c 15 mins