Preheat oven to 180℃.
In a large bowl, mix the dry ingredients together.
63 grams cocoa powder, 36 grams protein powder, 45 grams flour, 135 grams erythritol, 3 grams baking powder, dash of salt, ½ tsp instant coffee powder
Slowly add the diet coke.
300 grams diet coke, 1 tsp vanilla extract
Stir until no clumps remain.
Add the optional chocolate chips, or your favourite add-ins.
50 grams chocolate chips
Pour into a tin that's lined with baking paper.
Bake for 25 minutes, or until done.