Put the mushrooms in a heatproof bowl and pour 3 cups boiling water over the mushrooms. Leave to soak for 30 minutes. Drain the mushrooms through a sieve, reserving the liquid. Rinse the mushrooms thoroughly under running water to remove any grit, pat dry.

Preheat the oven to 350 degrees F. Heat the oil in a roasting pan on the stove top and add the onion. Cook for 2-3 minutes, or until the onions are softened. Add the rice and stir for 1-2 minutes, then add the mushrooms and stir. Pour in the mushroom liquid and mix well. Season with salt and pepper, cover with lid or foil. Bake in the oven for 30 minutes, stirring occasionally, until all the stock has been absorbed and the rice is tender. Serve immediately. Serves 4.