Clean the mushrooms and cut them into slices. Wash and drain the rice. Heat 3 tablespoons of butter in a deep pan and fry the finely chopped leeks and then the porcini mushrooms. Once slightly soft, add the rice, stir fry and top up with the wine.
Once the alcohol has evaporated, add spices to taste and transfer to a tray. Top up with around 4 cups of hot water or mushroom broth and put the dish to bake in a moderately heated oven until the rice absorbs all the liquid.