Naturally, Mademoiselle Ray’s little “snow mushrooms” are not available in the United States (or for that matter anywhere else in France), but I have found that our button mushrooms work extremely well prepared in this excellent way. The secret trick of the recipe is still valid. You expel their own water from the mushroom so that a tiny vacuum is created inside, and they suck in the aromatic butter and the attractively tart peasant-style egg and lemon sauce. (See