Preheat oven to 200°C
Mix butter, brown sugar, egg yolks and vanilla together
Add flour, baking powder and salt and mix well
Add chocolate chips and mix until combined
Tip the dough into an oven proof dish or foil roasting pan and press flat with your hands until evenly distributed
Bake for 20 minutes
If you want a harder/crispier cookie, leave in the oven for an additional 5 minutes
Remove from the oven and allow to cool before breaking or cutting into pieces
I have made this cookie non dairy with margarine and with oil. The margarine cookie had the same texture as the butter cookie but the taste wasnt as good. The oil cookie had a dryer texture to the butter cookie but tasted better than the margarine cookie.
They all tasted good but none were as good as the original butter cookie.