Mix orange juice, rosemary, 150 g melted butter and 2 tbsp. l. zest. Set aside. Boil a large pot of salted water, add the unpeeled onion and cook for 20 minutes. Drain the boiling water, pour the onion with cold water, let cool and peel.
Mix the onion with the remaining melted butter and zest, thinly sliced fennel, finely chopped garlic, cognac, salt and pepper. Wash the capon and dry it with a paper towel, rub inside and out with salt and pepper. Stuff it with an onion mixture, and cut a few onions in half and put them under the skin of the bird in the breast area.
Put the bird in a deep pan, pour in 1 cup of water. Thoroughly grease the capon with orange sauce and place in an oven preheated to 180ºС. Bake 1 hour 20 minutes, every 20 minutes. brushing with sauce. Remove the onions from the bird and place on a baking sheet. Add peeled carrots and mini patissons to the same place, mix with the sauce and cook for another 30-40 minutes. Remove the tray from the oven, let stand 15 minutes. and cut the bird. Serve with vegetables and the resulting sauce in a separate gravy boat.