Wash potatoes thoroughly and cook in boiling water for 20 minutes. In the meantime, wash quinces (to remove the fur), peel, quarter and cut out the core. Cut the quinces into pieces and sprinkle with lemon. Caramelise the sugar in a pot. Add quinces and apple juice, bring to the boil, season with a pinch of salt and simmer for 10 to 20 minutes. Wash duck breasts, pat dry and carve the skin crosswise.
Heat a flat roasting pan or an ovenproof pan without fat. Sauté duck breasts only on the skin side for about four minutes. Then fry on the meat side for two to three minutes. Season with salt and pepper. Roast duck breasts in the preheated oven (electric range: 200 °C/ convection oven: 175 °C/ gas: level 3) for twelve minutes. Wash the marjoram, shake dry and, except for something to garnish, add
Remove the duck breasts. Wrap them in aluminium foil and let them rest for five minutes. In the meantime, heat the fat in a pan and fry the potatoes for eight minutes, turning them over. Skim the fat from the duck with a tablespoon. Add 100 millilitres of water to the gravy, bring to the boil and season with salt and pepper. Remove the marjoram.
Stir the starch flour and two tablespoons of water until smooth. Thicken sauce with it, bring to the boil again. Remove duck breasts from the foil and cut into slices. Arrange on plates. Add potatoes and quince vegetables. Garnish with marjoram