1. Cut the chocolate and the butter into small pieces. Melt them in a double boiler until you have a homogeneous mixture. Remove from the heat.
2. Add the sifted flour to the melted chocolate.
3. In a bowl, whip the yolks with the sugar. Then add the chocolate preparation.
4. In another bowl, beat the egg whites with a pinch of salt. Gently incorporate them into the chocolate preparation.
5. Pour this mixture into a molded pan covered with parchment paper.
6. Bake for around 20 to 25 minutes in the preheated oven at 355 ° F. Watch the end of baking by pricking the cake with the blade of a knife: it should come out dry. Let the chocolate cake cool well before turning out.