Salmon Wellington

Preheat oven to 400ºF (200ºC).

Stuffing:
In food processor, whirl cubed halibut with egg white until smooth. Blend in whipping cream, lemon juice, chervil, salt and pepper. Refrigerate in airtight container for at least 1 hour or for up to 4 hours.

Cut salmon fillet crosswise into 1/2-inch (1 cm) thick slices; cover and refrigerate. Trim spinach, removing stems; rinse and shake off excess water. In large saucepan, cook spinach, with just the water clinging to leaves, just until wilted. Arrange in single layer on paper towels; pat dry.

On lightly floured surface, roll out puff pastry to form 14-inch (35 cm) square. Place on sheet of parchment paper large enough to cover large rimless baking sheet. Cover pastry with spinach, leaving about 1 1/2-inch (4 cm) border at edges. Spread half of the stuffing over spinach; layer with salmon slices, then remaining stuffing.

Mix egg yolk with 1 tablespoon (15 mL) water; brush some lightly on uncovered top and side borders of pastry. Starting at bottom edge and using paper as support, roll up, pressing egg-washed top edge onto pastry; fold in sides, pressing together lightly. Place roll and paper on rimmed baking sheet. (Make-ahead: Cover and refrigerate for up to 4 hours; add 10 minutes to baking time.) Brush lightly with egg wash. Bake in centre of oven for about 30 minutes or until golden and crisp.

Shallot Cream Sauce:
Meanwhile, in small saucepan, simmer shallots with vinegar over medium-low heat until vinegar is evaporated. Add cream; simmer until reduced by half, about 4 minutes. Whisking constantly, add butter, a few cubes at a time, to make creamy sauce. Add pepper.

To serve, trim off ends and cut pastry package crosswise into 8 slices. Pool one-quarter of the sauce onto each warmed plate. Arrange 2 slices per serving over and to side of sauce.