|Frozen fish fillets||1 Pound (Haddock, Flounder Or Ocean Perch, 1 Package)|
|Onion||1 Medium, sliced|
|Canned sliced mushrooms||3 Ounce (1 Can)|
|Tomato sauce||8 Ounce (1 Can)|
|Egg yolk||1 (Unbeaten)|
|Heavy cream||1⁄2 Cup (8 tbs)|
1) Thaw the frozen fillets as per package directions.
2) Separate the fillets and halve the large fillets.
3) In a large skillet, saute the onion, mushrooms, tomato sauce and parsley in melted butter.
4) Arrange the fillets side by side over the tomato mixture in the skillet.
5) Sprinkle the fillets with salt and pepper.
6) Bring the skillet mixture to a boil.
7) Cover the skillet, simmer over a low heat for about 10 to 12 minutes, until the fish is tender.
8) Transfer the fillets to a hot serving platter and keep warm.
9) Simmer the skillet liquid until it has reduced to about half in volume.
10) In a bowl, combine the egg yolk and cream, mix thoroughly.
11) Blend a little hot liquid with the cream, then return to the pan, stirring constantly.
12) Bring the mixture just to the boiling point and laddle over the fillets.
13) Garnish the Fillets Supreme with lemon wedges and parsley and serve immediately.