One preparation for 4 people gives about 300 g of duxelles. This mass is enough to fill 4 large mushrooms or for a small gratin.
Clean the mushrooms with a wet dish and chop them very finely, add the stems. Put this mushroom mixture in a dish and squeeze out the liquid. Cut the shallots into tiny pieces, sauté in butter and add the mushroom mixture. Season with salt, pepper and lemon.
If you like, take a little bit of garlic. The mushrooms soak up the butter very quickly, so maybe take a little bit more. Add the parsley and steam for 3 minutes until all the liquid has evaporated.
Season again. The puree should taste hearty.