How to cook
Wash the quinces, clean them and cut into pieces. Heat the butter with 3 1/3 tbsp (50 g) sugar and saute the quinces until softened.
Beat the eggs with the remaining sugar and vanilla, until you get a foam. Add the margarine, yoghurt with baking soda and citric acid. Finally, add the flour as well.
Stir everything until you get a homogeneous mixture. Put it in an oiled tray. On top, distribute the quinces and bake in a preheated 390°F (200 °C) oven about 40 min.