Preheat the oven to 210°C and line a baking tray.
Roll pastry to 5mm thickness and cut into two 40 x 25cm pieces.
Place 800g of salmon on one pastry sheet and cover with half the spinach.
Blend remaining 400g of salmon with double cream and half the chives into a purée.
Season the purée and spread it over the spinach.
Top with remaining chives, spinach, and brush pastry edges with egg.
Place the second pastry sheet over the salmon and seal the edges firmly.
Trim excess pastry, brush the entire parcel with egg, and season.
Bake for 40-45 minutes until the pastry is golden and salmon is cooked.
Toss vegetables with olive oil and seasoning, then roast for 25-35 minutes.
Boil shallots, vinegar, and wine until only 2 tablespoons remain.
Add 1 tablespoon water and simmer until 1 tablespoon remains.
Gradually whisk in butter cubes on low heat until emulsified.
Strain the sauce, stir in chives, and season.
Carve the salmon into thick slices.
Serve salmon with roasted vegetables and a drizzle of sauce.