Preheat the oven to 450F. Butter your ramekins or tins, then dust them with cocoa powder.

Put about an inch of water in a small pot and heat it over medium heat until it’s bubbling and steaming. Then place a heat proof bowl (glass or metal) over it with the chopped chocolate and butter, cut into chunks, in the bowl. Stir it occasionally until almost all of the butter and chocolate is melted, then remove it from the heat and continue to stir until all of it is melted. Set the mixture aside to cool, but not harden. Once it has cooled, stir in the vanilla extract and chocolate.

In a mixing bowl with an electric hand mixer or the bowl of a stand mixer fitted with a whisk, beat together the eggs, egg yolks, and sugar until the mixture is thick, pale, and fluffy. This should take 5-7 minutes, and it will run off the beater in thick ribbons.

Slowly add the chocolate and butter into the eggs on low speed until thoroughly combined, then add the flour and stir for a few seconds or until just combined.