Finely crush the spices in a mortar. Score the skin of the duck breast in a diamond shape. Rub with the spices on both sides. Wrap in plastic wrap and place in the refrigerator for one night, weighted down with a plate.
Preheat the oven to 225 °C. Season the meat with salt on both sides and brown skin side down in the Reindl. Then turn to the other side. Add the onions and sauté. Extinguish with water and the juice that has formed during marinating. Place the Reindl in the preheated oven and cook for 15 to 20 minutes with the lid closed. Remove the meat and keep warm.
Remove any excess fat from the stock. Add the crème fraîche. Stir the cornflour with 4 tbsp water, add to the sauce and bring to the boil. Season with salt, pepper and sugar if necessary.
Tip: Always use aromatic spices to refine your dishes!