Preheat the oven to 230 degrees C. Butter and flour cake tin or 4 ramekins.
In the top half of a double boiler set over simmering water, heat the butter and the chocolate until chocolate is almost completely melted. If you don't have a double boiler, just use a pan of boiling water, put a smaller pan on top of it, add chocolate to it and let the steam from boiling water melt it.
Use a hand held electric mixer to beat the eggs, egg yolks and sugar together until light coloured and thick.
While beating, slowly pour the chocolate mixture into the egg mixture, then quickly beat in the flour and mix until just combined.
Divide the mixture between the 4 ramekins and bake for 6 to 7 minutes. The centres of the cakes will still be quite soft. Turn ramekins out on serving plates and let sit for about 15 seconds, then unmould. Serve immediately with fresh cream, if desired.