This is an ideal dish for entertaining, as you can assemble the croûte ahead and chill it before baking. The combination of crisp pastry, succulent salmon, and watercress sauce is a real winner.
Serves 8
3 tbsp olive oil
3 shallots, finely chopped
7 oz (200 g) crimini mushrooms, finely chopped
3 garlic cloves, finely chopped
1 tbsp lemon juice
41⁄2 oz (125 g) watercress, chopped
salt and freshly ground black pepper
2 tbsp full-fat crème fraîche
1lb 10 oz (750 g) store-bought puff pastry (preferably all-butter)
2 pieces skinned salmon fillet, each 1lb 2 oz (500 g)
1 tbsp hot horseradish sauce
1 egg, beaten
For the sauce
2 tbsp (20 g) butter
1 shallot, finely chopped
2 tbsp (15 g) all-purpose flour, plus extra for dusting
13⁄4 cups (400 ml) vegetable stock
31⁄2 oz (100 g) frozen peas
31⁄2 oz (100 g) watercress, chopped
5 tbsp full-fat crème fraîche
1 tbsp finely chopped fresh mint
1. Heat 2 tablespoons of the oil in a large, nonstick frying pan. Add the shallots and fry over medium heat for 3–4 minutes or until softened, stirring occasionally. Increase the heat to high, stir in the mushrooms and garlic, and fry for 4–5 minutes or until the liquid has evaporated. Add the lemon juice. Take the pan off the heat and mix in the watercress until wilted. Season, transfer to a bowl, and set aside to cool, then stir in the crème fraîche. Preheat the oven to 425ºF (220ºC).
2. Roll out half the pastry on a lightly floured surface. Trim to a rectangle 2in (5cm) larger all around than the salmon. Wrap the pastry trimmings in plastic wrap and set aside. Place the rolled-out pastry on a large piece of parchment paper that will fit on a large baking sheet or in a shallow roasting pan. Lay one of the fillets in the middle of the pastry. Season and spread the horseradish sauce on top, then the mushroom and watercress mixture. (See Make a well-sealed parcel, steps 1 and 2.) Lay the other fillet on top. Season.
3. Roll out the remaining pastry to a rectangular shape that is about 3in (7.5cm) wider and 2in (5cm) longer than the bottom pastry layer. Brush the edge of the bottom layer with the beaten egg. Lay the pastry over the salmon and trim off the excess to give a 3⁄4in (2cm) edge all around. Press, score, and crimp the edges. Reroll the pastry trimmings thinly and cut them into strips. Brush the croûte all over with egg, lay the strips on top in a decorative pattern, and brush these with egg. (See Make a well-sealed parcel, steps 3 and 4.)
4. Carefully lift the croûte onto a large baking sheet, with the parchment paper still underneath. Bake for 30 minutes or until the pastry is golden brown. (See Bake the croûte to perfection.)
5. Meanwhile, make the sauce: melt the butter in a medium pan. Stir in the shallot and fry for 2–3 minutes or until softened but not browned. Stir in the flour and cook for 1 minute. Take the pan off the heat and slowly stir in the stock. Return the pan to the heat and cook, stirring, over medium–high heat, until the sauce has thickened slightly. Add the peas. Simmer for 2 minutes.
6. Remove the pan from the heat and stir in the watercress. Purée in a food processor until smooth. Pour the sauce back into the pan and set aside. When the croûte is done, remove it from the oven and let it rest for 10 minutes. Meanwhile, stir the crème fraîche and mint into the sauce, season, and reheat. (See Make a bright green sauce.) Transfer the croûte to a board or serving platter and serve in slices with the sauce.
SALMON EN CROÛTE WITH WATERCRESS SAUCE
KEYS TO PERFECTION
Make a well-sealed parcel
1 It’s important to roll out the pastry so it’s not too thick, as it needs to cook in the same time as the fish (the fish will become dry if overcooked). Roll it out so it’s about 1⁄4in thick—that way, it will bake up light and crisp. The first piece of pastry (for the bottom of the croûte) should be 2in (5cm) larger all around than the size of a salmon fillet.
2 Spoon the mushroom and watercress filling carefully over the length of the bottom salmon fillet, then spread it out using a palette knife or round-bladed knife. Go almost up to the edge but not quite all the way, otherwise when you place the second fillet on top the weight of it may cause the filling to ooze out. Place the second fillet on top of the filling and season.
3 To make sure you don’t stretch the pastry while covering the top of the salmon, lay it over a rolling pin to make it easier to lift and lower onto the fish. Press down the pastry edges well, or the filling may leak out when baking, then score the edges to secure the seal by gently tapping all around the cut sides using the back of a knife held horizontally.
4 Crimp the edges using your fingers. Reroll the pastry trimmings thinly and cut out 10–12 strips in 2 or 3 different sizes, varying from 1⁄2in (1cm) to 1in (2.5cm) wide and long enough to go over the domed part of the croûte. Trim to fit. Brush the croûte all over with beaten egg, then lay the strips over in a criss-cross pattern (you may not need all the pastry trimmings). Brush the strips with egg.
Bake the croûte to perfection
1 Transfer the pastry-wrapped salmon to a large baking sheet with the help of 2 fish slices to keep it stable. Retain the parchment paper underneath, as this will prevent the pastry from sticking to the sheet and make it easier to move once baked.
2 Baking the croûte at a high oven temperature will make the pastry light and crisp, especially on the base, and ensure that the salmon is cooked through. However, as the temperature is high, check after 20 minutes—if the pastry is already turning brown, lay a piece of foil loosely over the top to protect it from becoming overdone while the salmon finishes cooking.
Make a bright green sauce
1 Watercress can quickly discolor if heated for too long, so to keep the sauce a good green color, stir in the watercress off the heat: the heat of the sauce and pan will be sufficient to wilt the watercress while maintaining its color. The peas will also help to boost the color.
2 After puréeing the sauce, pour it back into the pan. Before serving, place it over low heat and stir in the crème fraîche, mint, and salt and pepper. Heat through for as short a time as possible. As with the watercress, you want to retain the fresh green color of the mint.