Soak the beans overnight. Put them to boil in new water the next day, until softened.
Start arranging it in layers in the clay pot, alternating between it, the onions cut into crescents and slices of peeled tomatoes.
Sprinkle each layer lightly with salt and chopped spearmint. Pour on the oil, a little of the broth in which you boiled the beans and place the clay pot on low heat in the oven.
Cook until ready.