Break the dark chocolate couverture into pieces, place in a saucepan, place on a saucepan filled with water and let it melt.
Mix the flour and cocoa powder.
Beat eggs with sugar in a mixing bowl until thick and frothy.
Melt 170 g butter in a saucepan and mix with the dark chocolate couverture. Add the chocolate-butter mixture in a thin stream and whisk in. Finally stir in the flour-cocoa mixture and the salt.
For the dessert molds: melt about 2 tablespoons of butter in a saucepan. Grease the molds with it and dust with 2 tablespoons of cocoa powder. Spread the batter over the molds and cover the molds overnight in the refrigerator.
The next day, preheat the oven to 180 ° C top / bottom heat. Place the molds on the oven shelf and bake the cakes on the middle rack for about 20 minutes, then tip out of the molds. Arrange chocolate cakes with a liquid core on plates. Place a cake fork on the edge of the plate and dust with cocoa powder. Serve immediately.