Preheat the oven to 180 degrees.
In a large mixing bowl cream together the melted butter and sugar for a few minutes until light and fluffy.
Add the eggs one at a time whilst mixing, then add in the vanilla, baking powder, flour and cocoa powder until fully combined.
Fold in the chocolate chips (optional).
Line a 18 x 28cm tin with baking paper and spread the mix evenly.
Bake for 25-30 minutes.Brownies should spring back when touched!