Preheat the oven to 150 degrees top / bottom heat.
Break the chocolate into pieces and melt together with the butter either in the microwave on the lowest setting or in a water bath. Add the sugar and stir everything into a homogeneous mass. Let cool down briefly.
In the meantime, separate the eggs and beat the egg whites into stiff snow. Then gradually add the egg yolks to the chocolate mass, as well as the flour (40 grams is not a typo!). At the very end, carefully fold in the egg whites.
Line the bottom of a 28 centimeter baking pan with parchment paper, pour the batter into the pan and put it in the oven. The cake is ready in 40 to 45 minutes - no longer, it should still be juicy on the inside.
This is an original recipe from Toulouse and just a chocolate dream!