Fry the onion, finely-chopped, and the other vegetables, diced, in 8 tablespoons of oil over medium heat, stirring often with a wooden spoon.

Keep the pot covered so that the vegetables "sweat" in their own juice as long as possible. As soon as you see that the juice seeping out is no longer sufficient, add enough water to completely cover them. Leave to cook slowly for about an hour, with the lid on, seasoning with salt and pepper.

Then add the rice and boiling water to submerge everything again. Stirring frequently, simmer gently for another 15 to 20 minutes.