If you use the fillet, cut it into 1-inch-thick slices. If you use chops, make about 4 double cutlets. Sprinkle the slices with salt and dredge them with flour. (There should be about 1tablespoon flour left.)
Melt lard in a frying pan and fast-fry the venison slices on both sides. Place the fried slices on the bottom of a heavy casserole and set aside.
Fry onions in the same frying pan till golden in color. Then add 1tablespoon cold water and the paprika. Cover the pan and cook till liquid is evaporated.
Add cooked onions to the meat and pour in 2 or 3tablespoons of meat stock. Cover tightly and cook over low heat till boar is half done. Add more stock if needed.
Clean wild mushrooms but leave whole. Cook in the same lard in the same frying pan for 1 minute. Remove mushrooms with a slotted spoon and add to meat casserole. Cover casserole again and cook for 30 minutes longer.
Mix remaining 1tablespoon flour with sour cream and mix into meat casserole. Simmer for a few minutes longer.