Melt the 330g chocolate and butter in a bain-marie or in the microwave using short bursts and lots of stirring. Don’t let it get too hot or the chocolate will split. Low and slow FTW.
Beat the eggs and sugar in another bowl until combined.
Pour the chocolate mixture into the egg mixture and mix until just combined. Add the dry ingredients - cornflour, cocoa powder, baking powder and any add ins you're using.
Rest this batter for an hour in the fridge until it’s set.
Preheat the oven to 160°C fan/180°C. And line two baking sheets with parchment paper.
Scoop the dough into 50g portions and roll into balls. Get your hands dirty. At this point, you can put the dough balls back in the fridge or in the freezer. They’ll keep in the fridge for two days or the freezer for a month.
Make sure the balls are spread out on your baking sheets. Bake for 12 minutes or 13-14 minutes from frozen.
Remove and sprinkle with salt while they are warm. Cool on the baking sheet before trying to move them.