Salmon and spinach en croute

Name: Salmon and spinach en croute
Cook time: 1 h
Total time: 1 h
Cuisine: Mediterranean, French, European, British
Ingredients: 2 sheets of puff pastry; 700g of salmon fillet, skinless and boneless; 2 egg yolks, beaten, to glaze; salt; freshly ground black pepper to taste; 600ml of milk; 50g of butter; 100g of plain flour; 150g of cheddar, grated (or a similar hard cheese); 200g of baby spinach leaves, roughly 2 bags; 60g of pine nuts; 1 garlic clove, crushed or grated; olive oil