Preheat oven to 190 C; 375 F, Gas mark 5. Grease a shallow casserole dish. Drain can of salmon, flake and set aside. Arrange one third of potatoes and half of leeks in casserole dish. Add half the salmon then a further third of potatoes and remaining leeks and salmon. Sprinkle over the cheese and cover with remaining potato. Mix the milk, fromage frais and 1 tablespoon of oil. Season. Pour into casserole. Brush top layer with remaining oil, cover and bake for 45 minutes. Remove cover. Continue baking until brown. Serves 6. Approx. 260 kcals per serving