Cut the stem tops of each quince into small pieces and remove the core. Hollow out the quinces until a layer about 15 mm thick remains.
Fry the mince together with the onion. Season with salt, pepper and cinnamon. Fill the quinces with this mixture. Cover with the stem lids and arrange them in a wide cooking pot.
Pour warm water over them until a third of the quinces are covered. Sprinkle with sugar and cook on low fire. Be careful not to overcook the quinces.
Remove from heat and thicken the sauce with egg yolks.