Pour 1 1/2 cups of water into a large frying pan and add the wine, stock, spring onions and peppercorns. Put the salmon fillets in the pan in a single layer. Bring to the boil, then immediately reduce the heat, cover and simmer gently for 5–6 minutes until the fish flakes when tested with a fork.
Meanwhile, to make the sauce, stir together the sour cream, cucumber, dill and lemon juice in a bowl and season to taste with salt and pepper.
Arrange the salad leaves on four serving plates. Carefully lay the salmon fillets on top, using a slotted spoon. Drizzle a little of the sauce over the top and serve with lemon wedges and some sprigs of dill for garnish.