It takes some time (and an assortment of pots and pans) to make this, but your efforts will not be in vain. --Chez Pierre at the Charlotte Inn, Edgartown (Martha's Vineyard), Massachusetts
2 pounds spinach
4 cups heavy cream
Salt and pepper
6 very large white mushrooms (Pennsylvania-type)
4 pounds filet of flounder (or other white-flesh fish such as sole)
6 scallions, julienne
2 to 3 cups dry white vermouth (just enough to come halfway up sides of fish)
4 shallots, coarsely chopped
Puff pastry crescents (optional)
Clean spinach. Steam in a small amount of water, drain, and puree. Set aside and keep warm. In a pan, bring heavy cream to a soft boil and allow to reduce in volume by half. (This may take a while.) Gradually add reduced cream to spinach puree until desired thickness and color of sauce is obtained. (Keep in mind that sauce will thin out when fish is added.) Add salt and pepper to taste and keep warm. Slice each mushroom individually in thin slices (about 8 slices) and place in order of slicing down the entire length of each filet of fish. Top each filet with julienne scallions.
In a large pan, bring vermouth and shallots to a simmer (thyme, parsley, and a slice of onion may be added to enhance the poaching liquid). Place fish filets in simmering liquid, cover, and cook at about 180 degrees F (liquid should be "trembling," not actually simmering) until fish is just cooked through, about 3-5 minutes depending on thickness. Ladle spinach cream sauce onto individual warmed plates. Carefully remove each filet with slotted spatula, tipping against a paper towel to drain excess moisture. Then lay gently on the spinach sauce. Garnish with puff pastry crescent if desired. Serve immediately.