Preheat oven to 375°F. Pull off the skin of the duck breasts, then bone them. Cut meat into 1-inch squares.
In a heavy Dutch oven melt half of the fat and wilt the onion in it.
Add duck meat and sliced vegetables to the onion and sauté for a couple of minutes. Add 1tablespoon water and cover. Cook the duck; keep adding tablespoons of water until duck is cooked. Do not have a lot of liquid at any time.
If mushrooms are small buttons, leave them whole; if larger, cut into pieces.
In a second pot melt the rest of the fat. Add mushrooms, rice, parsley and peas, and cook over medium heat for a few minutes. Stir and cook over low heat for a few more minutes till the ingredients are coated with fat.
Add rice mixture to cooked duck meat, together with salt, pepper and marjoram. Add 2cups water and bring to a boil under a heavy tight-fitting lid.
Bake in the preheated oven for 25 minutes.
Place the duck and rice on a serving platter and decorate it with sautéed duck livers and duck cracklings made out of the fat.