Add half the cocoa, stir it all together and give the mixture a good sniff. If it doesn’t smell chocolate enough, add the remaining cocoa. You might like even more than the 40g here, in which case, feel free to add another 10g or so.
Put all wet ingredients in a jug and whisk the egg.
Stir the two together until just combined and there is no dry flour. Lumps don’t matter. Don’t over mix, or the muffins will be tough.
If using, put a muffin case in each of the holes of a 12 hole muffin tin.
Divide the mixture evenly between the cases and bake at 375-400F / 190-200C / gas mark 5-6 for 20-25 minutes until the tops spring back when gently pressed.