Serves 8 to 10.

Batter for Giant Crêpe

1/3 cup of flour
1/2 cup of milk
1 large egg
1 Tbsp of cooking oil / 1/2 tsp of salt

Pâte à choux

1-1/2 cups water in 2 1/2 quart saucepan
1-1/2 sticks of unsalted butter cut into pieces
1-1/2 tsp of salt
1 cup of flour
6 large eggs

Filling

2 lb of sole fillets (16 fillets each about 9×2 inches)
1/2 lb skinless and boneless halibut or more sole fillets
1 cup of heavy cream
10 oz of mushrooms
Several shallots
Salt, pepper, nutmeg, some additional butter

• Arrange about 3 layers the fillets with sprinkling of minced shallots, salt and pepper and a few drops of Cognac.
• Refrigerate.

• For the Giant Crêpe, place flour in a bowl and make a hole in center.
• Add the egg, oil and salt.
• Beat together and slowly incorporate the flour as you add the milk.
• Let rest for 1 hour.
• Preheat oven to 400°F.
• Smear a sturdy jelly roll pan with butter, roll flour in it.
• Put a thin layer of crêpe batter into pan and set in lower oven for 4 or 5 minutes or until set.
• Then place under the broiler to brown top slowly and lightly.
• Slide crêpe off into a cake rack.
• Refrigerate between two sheets of wax paper.

• For the pâte à choux, bring 1-1/2 cups of water to boil with the cut up butter and salt.
• As soon as the butter has melted, remove from heat and dump in all of the flour at once.
• Beat  vigorously until smooth.
• Set again over high heat beating continuously to evaporate excess moisture.
• Scrape paste into a mixer.
• At low speed, incorporate 5 eggs one after another.
• Break sixth egg in a small bowl, beat it, and add it to the mixture by droplets, only as needed, so that the mixture holds its shape.
• Remove 1/2 cup and refrigerate for fish mousse.
• Set the rest in a bowl over warm water for final assembly.
• For the fish mousse, cut the halibut and one of the sole fillet into chunks.
• Place in the food processor with cold choux paste, 3/4 cup of chilled cream, 1/2 tsp of salt, grinds of white pepper, pinch of nutmeg.
• Ground into a fine paste.
• If too stiff add more cream, but it should hold its shape.
• Cover and refrigerate.
• For the mushroom duxelles, mince mushrooms by hand or in food processor.
• Sauté in frying pan in 2 Tbsp of melted butter with some minced shallots for 4 to 5 minutes.
• Season lightly with salt and pepper and pour in 3 Tbsp of Cognac.
• Boil down rapidly to evaporate liquid.
• Scrape into a bowl and reserve.

Assembling the Choulibiac

• Spread the Giant Crêpe on a buttered baking dish (nonstick if possible) and trim off any stiff edges.
• Spread 1/3 of the fish mousse in a rectangle about 12 x 5 inches and arrange half of the fillets over it.
• On top of that, spread half of the duxelles, then the rest of the fillets and remaining duxelles.
• Beat any fish-seasoning juices into reserved mousse and spread it over top and sides of fish structure.
• Then, bring the ends and sides of the crêpe up over the fish, trimming off any crêpe in excess of 1 inch edging.
• Reserve half cup of choux paste for decoration; then, using a flexible spatula dipped in cold water, spread choux pastry evenly over top and sides, masking structure completely.
• Poke holes in the lower part of the four corners and insert buttered foil funnels.

Decoration and baking

• Preheat oven to 425°F and set rack in lower-middle level.
• If choux paste has cooled and stiffened, beat over warm water.
• Spoon in pastry bag with half inch cannelated tube.
• Paint Choulibiac with a coating of egg glaze then decorate as you wish.
• Reserve 5 or 6 Tbsp of choux pastry for velouté sauce.
• Glaze the decorations and the rest of the pastry with two coatings of egg.
• Immediately set in oven and cook for 15 to 20 minutes until pastry is slightly brown and puffy.
• Turn oven down to 375°F and continue baking another 20 minutes.
• Serve as soon as possible with a velouté sauce.

Velouté sauce

2 cups of fish trimmings
1 onion, 1 carrot, 1 celery stalk, chopped
parsley, bay leaf
1 cup of white wine, 1 cup of water, 1/2 tsp of salt
5 to 6 Tbsp of choux pastry
1 cup of milk, 1/2 cup of cream
white pepper, lemon juice, butter (as much or as little as you wish)

• Simmer the fish trimmings with the vegetables, herbs, wine, water, salt for half an hour.
• Strain, then boil down rapidly to 1 cup.
• Gradually blend in the choux pastry, pour into saucepan and simmer thinning out as necessary with spoonfuls of milk and cream.
• Sauce should coat a spoon lightly.
• Season with salt, pepper and lemon juice.
• Add additional butter if you wish.