Make very thin, light pancakes in a pan about 6" across.
Wash, but don't peel the mushrooms: slice the heads, chop the stalks.
Fry the chopped mushroom stalks gently for 10 minutes in 2 tablespoonfuls of butter, then add the sliced heads and fry for a further 5 minutes in a pan with a lid on.
Then sprinkle with flour, season, stir in hot milk; cook gently for 20 minutes.
Put some of this thick mixture of mushrooms and sauce on each of the pancakes.
Roll them up, arrange them in a fireproof dish, cover them with melted butter, and brown in the oven for a few minutes.
garnish as desired.