Put the mushrooms in a bowl with the water and leave to soak until the mushrooms have softened. Drain, reserve the liquid and finely chop the mushrooms. Set aside until needed.

Melt the butter and oil in a large, heavy based pot and sauté the onions and garlic for a few seconds. Add the rice and stir until all is combined. Mix in the saffron.

Gradually stir in the hot stock and reserved mushroom liquid one ladle at a time, only adding the next ladle once the liquid has been absorbed. Continue until the rice is al dente.

Mix in the mushrooms and Parmesan and serve sprinkled with extra Parmesan.