Rinse deer steaks and place in a zip bag with vinegar and water; allow to soak for 2 to 3 hours in the refrigerator. Remove steaks and discard vinegar water; rinse out bag. Rinse meat; trim and debone. Place back in bag and cover with milk. Allow to marinate for at least 4 hours in the refrigerator.
Remove meat from refrigerator about 1/2 hour before cooking. Drain milk from meat but do not rinse again. Pat dry.
In a flat bowl or dish, combine the flour, salt, black pepper and garlic powder.
Heat oil in a large, heavy pan. Dredge steak pieces in seasoned flour.
Brown deer steak in oil. Remove steak and place in a covered casserole dish.
Add onions to pan and sauté until tender, remove to the casserole dish. Add 1 can beef broth to the frying pan. Bring to a boil and scrape the bottom of the pan. Reduce heat.
Add the butter to the pan and stir to combine. Dump in the flour left in the dredging dish, stirring to incorporate. Add the second can of broth, the Worcestershire and the wine; cook until gravy begins to thicken. Salt and pepper to taste. Pour or ladle gravy over venison and onions; cover casserole dish and bake for 45 to 60 minutes.
Serve with salad and rice. We also prepared mashed cauliflower with the dinner.