Heat the remaining oil in a frying pan over a medium heat. Add the leek and fry for 5 mins, or until beginning to soften. Stir through the garlic for 1 min, then add the cream, capers and 75ml hot water, then bring to the boil. Stir through the chives.
Heat the grill to high. Pour the creamy leek mixture over the potatoes, then sit the salmon fillets on top. Grill for 7-8 mins, or until just cooked through. Serve topped with extra chives and capers and a salad on the side, if you like.