Peel and finely grate the ginger. Mix with jam and soy sauce. Clean and wash the Brussels sprouts. Wash duck breast fillets and dab dry. Cut the skin with a sharp knife in a diamond shape.
Season the meat side with salt and pepper. Brush an ovenproof pan or a flat roasting pan with a little oil and heat it up. Sauté the fillets in it on the skin side for about 5 minutes. Turn and fry briefly on the meat side.
Roast in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2) for approx. 20 minutes. After approx. 10 minutes brush with half of the jam mixture.
Cover the Brussels sprouts and cook in boiling salted water for 15-18 minutes. Peel and finely dice the onion. Remove duck breast fillets and let them rest loosely covered for about 5 minutes. Drain the duck fat down to approx. 1 tbsp.
Heat the rest of the jam mixture in a roasting pan. Stir in the stock, bring to the boil and boil down for about 5 minutes.
Heat butter in a pot and sauté onion. Drain the Brussels sprouts and toss in the onion butter. Stir the starch and 2 tablespoons of water until smooth, thicken the sauce with it. Season with salt, pepper and 1 pinch of sugar.
Take the fillets out of the foil, pour the escaped meat juice into the sauce. Cut duck breast into large pieces. Serve with sauce and sprouts, garnish with thyme. Croquettes taste good with it.