Chop 100 grams of dark chocolate and place in a saucepan. Melt in a bain-marie. Cut 100 grams of butter into cubes. Add the chocolate and mix with a wooden spoon until forming a smooth cream. Break 4 eggs in another saucepan and beat them with an electric whisk together with 100 grams of sugar, until you get a frothy dough. Add a little at a time 50 grams of flour taking care to mix gently with a wooden spoon or a whisk. Pour the melted chocolate into the egg and sugar dough, stirring slowly with the wooden spoon. The mixture must be perfectly smooth and homogeneous. Butter and flour 10 small aluminium moulds. Fill them by three quarters with your preparation. Cook for about 5-6 minutes in a preheated oven at 200 ºC. Remove them, put them on a serving plate and serve immediately.