Peel and quarter the onion and process with the peeled garlic cloves until everything is finely chopped. Heat the oil in a large wide pan and cook the onion and garlic mush until softened, but not colored.
Remove the stalks from the shiitake and slice them; quarter the button mushrooms and slice them too. Slice the cremini mushrooms, and peel and quarter the inky field mushrooms, discarding the stalks first.
Add the butter to the pan and tumble in the mushrooms when it has all but melted. Try and turn the mushrooms in the pan, although this will be difficult, I know, as even a big pan will be extremely full. Put a lid on the pan and cook the mushrooms for about 15 minutes. Stop at this point if you’re cooking ahead of time.
Take off the lid (reheat first if you’ve done the above bit earlier) and add the salt, sherry, paprika, nutmeg and sour cream. I don’t think this needs pepper, but by all means add it if you want to. Stir this deep, creamy buff-colored and nubbly mixture on the heat for about 5 minutes, add most of the parsley, stir again, then put it on whatever dish you’re serving it from and sprinkle over the rest of the parsley.
I’d use 2½ cups basmati rice here. Cook according to package instructions. I have to say I am a firm believer in electric rice cookers (and see page 243 for a full enthusiastic exegesis on the subject) but don’t want to get into my salesman’s patter here. Whichever way you’re cooking the rice, lightly press on 3 cardamom pods with the side of a knife, just to crush them slightly first, and chuck them into the water along with the rice. I don’t salt my rice, finding the richness and depth of the aromatic and creamy mushrooms flavor enough. The cardamom provides musky fragrance, which is all this rice – beautiful in its plainness – needs.