Wash the rabbit very well and salt it. In a small pot, braise the onions, rabbit offal with the rice, spearmint and black pepper.
Add a little water and boil it just a little bit. Remove from the stove and stuff the rabbit with this mixture but set aside 1 cup of rice. You can add a few mushrooms if you like.
Sew the rabbit closed and put it in a rectangular tray. Separately, chop more onions and add them to the tray with water, a little oil and salt.
Cover with aluminum foil and bake about an hour. Take it out of the oven and put the remaining rice in to take in water and cover with the foil again.
Finally, bake briefly without the foil until reddened.