RECIPE:
Oven at 180C or 350F
Melt the butter in a big saucepan, then take off the heat and stir in the sugar.
Briskly stir in the eggs, then add the sifted flour/cocoa powder/baking power.
Once all combined, add your 'extra' (see ingredients) and stir through.
Pour into brownie or slice tin, and bake for 15-20 minutes until a skewer comes out almost clean, but not quite. You want this a little bit chewy.
Note: if you're adding peanut butter or nutella for example, it's easier to swirl this through the top once the plan batter is in the pan.