Peel onion and apple, cut into segments. Place into the baking form, add rosemary, port-wine, orange juice and broth. Slice goose breast and fry in the pan until light-brown. Season with salt and pepper, place into the pan. Bake in the oven at 80 degrees Celsius for 7 hours. Remove the goose and increase the heat to 220 degrees Celsius. Bone the meat, drizzle with salted water. Bake for about 10 minutes until golden brown. Strain goose fat from the roasting pan, add orange zest, soaked starch, bring to the boil, stirring, season with salt and pepper. Slice the breast and serve with sauce.