Portion the chicken (wings, legs and white meat), leave the backbone whole. Wash them very well and put in a pot.
Pour in cold water and add salt (1 tsp salt for every 4 1/5 cups (1 L) water). Once it reaches boiling point, remove the resulting foam. Chop 1 onion head finely and add it to the boiling chicken along with the black pepper grains and whole pepper and carrot. Boil until the meat is semi-ready.
In the meantime, wash the rice very well under running water while rubbing the grains in between your palms. Then put them in a bowl with slightly salted cold water.
Chop the other onion head finely. Heat the oil in a pan and braise the onions briefly, add the rice and braise about 3-4 min.
Distribute the braised riced evenly in a tray, distribute the portioned meat (without the backbone) on top.
In the bowl/cup in which you measured out your rice, pour broth from the chicken and pour it into the tray; do this 3 times.
Salt to taste if needed. Chop the butter into cubes and distribute them evenly on top. Put the tray in a preheated 356°F (180 °C) oven and bake until the rice is ready - about 40 min.
Take the tray out of the oven and wrap it with a clean, dense towel, to smother it for 10-15 min.
From the boiled chicken backbone, along with the pepper, carrot and remaining broth, make a chicken soup.