Marinate the rabbit Day 1. Bring all the ingredients for the marinade to a boil, then let cool to room temperature. While the marinade is cooling, cut up a hare into serving pieces. Find a covered container (plastic, ceramic, glass) just about large enough to hold the cut-up hare and put the meat inside. Cover with the cooled marinade. If you have leftover marinade, put that into a different container. Put everything in the refrigerator and let it sit at least 8 hours, but 2 days is better.
Day 2: Remove the hare from the marinade and pat it dry. Save the marinade. Heat the butter in a large, heavy pot with a lid. Dredge the hare in the flour and brown well on all sides. Do this over medium to medium-high heat so the butter does not burn. Remove the hare pieces as they brown and set aside.
As the hare is browning, preheat your oven to 325°F and strain the marinade into a bowl.
Once you've browned the hare, add the onion and stir to coat with the butter. If there is not much butter left, add another tablespoon or so. Cook the onions over medium-high heat until they are soft and a little brown on the edges. Sprinkle salt over them as they cook.
Return the hare to the pot and add the strained marinade. Bring to a simmer, cover and put into the oven. Cook until the meat wants to fall off the bones: This will take 2 to 4 hours for a wild hare, or between 90 minutes and 2 hours for a store-bought rabbit.