Trim the stems off the mushrooms, removing any woody parts, and cut into thin slices.
Put the rice, water, salt, soy sauce, mirin, sake and mushrooms in a pan and cover.
Bring to a boil, reduce to a simmer and cook until the liquid has been absorbed and the rice is cooked. Serve warm.
Notes
Many recipes use a rice cooker to cook this - if you choose to do so, the method is much the same but liquid level and timing should be as per rice cooker's instructions. Add the mushrooms after getting the liquid level right.