Season the rabbit pieces with salt and pepper and fry in butter until a brownish-red crust forms (the meat does not have to be cooked through at this point).
Remove from the pan and place on the bottom of a Dutch oven or a heavy casserole.
Return the pan to the heat and saute the onions (adding more butter, if necessary), until they are tender and slightly golden, about 10 minutes.
Drain the onions on paper towels and add to the rabbit.
Whisk together sour cream, wine, and brandy.
Pour over the rabbit and onions.
Bring to a simmer and season with salt, pepper, and nutmeg.
Add the bay leaf, cover, and simmer over low heat for 45 minutes.
Serve with pan-fried potatoes.