If that was the only way to get mushrooms, they'd be permanently off the menu for most of us. I lose patience with those who insist it's hardly worth eating veges that aren't gathered from the wild (ha!), home-grown, or, at the very least, organic. We're much better off being able to buy different kinds of cultivated mushrooms locally than not having them at all.
I used to think there wasn't all that much food value in these strange fleshy fluted things, but apparently I was wrong. They're about 85 percent water, but they're also high in fibre and rich in potassium, phosphorus, magnesium, iron and calcium, as well as in vitamins B1, B6, C, H, and folic acid (which is rare in most veges). So there.
My favourite way to eat the biggest, fattest ones is creamed, on or with buttered toast. You start with a basic white sauce (béchamel sounds better), and as you add the mushrooms they release their juices and turn it a marvellous dark stormcloud colour. It's a very simple dish, perfect for brunch or lunch, but it does need to be carefully made to taste as it should.
Creamed mushrooms with toast
As many big black mushrooms as you need - at least 4 for 2 people, depending on mushroom size
30 grams butter
30 grams plain white flour
About 450 ml (1 and a 1/2 cups) milk (full milk is best, but trim will do)
salt and freshly ground black pepper
splash of brandy (if you're feeling extravagant)
Remove tough ends of stalks and cut the mushrooms into chunks (roughly 2 cm square). Place in ceramic or glass microwave dish, cover and microwave for 1-2 minutes on medium high, just to soften them. (You can skip this step, but I find it helps commercially grown mushrooms cook more easily in the sauce later.) Set aside.
Heat the milk in a large glass jug in the microwave, in 30-second bursts on high, until it's close to boiling (watch it). Melt the butter in a heavy-bottomed saucepan over the lowest possible heat. Take off the heat and rapidly stir in the flour, using a wooden spoon. Return to heat and cook gently, stirring all the time to keep lumps at bay, until (says Julia Child) "the butter and flour froth together for 2 minutes without colouring". Take the pan off the heat and slowly pour in the hot milk, stirring madly as you go. Put pan back on low heat and cook the mixture gently, stirring all the time, until it thickens to a smooth sauce. If it seems to be getting too thick, add more milk, a little at a time (but see note about mushroom juice below).
And if there's a bit left over, I add more milk and some mushroom powder (or, dare I say it, a packet of mushroom soup - Julia would kill me, but too bad), blend it and turn it into nice soup for a weekday lunch.