Set an oven rack 6" beneath the broiler. Preheat the broiler to high. Combine the eggs and cream in a bowl. Mix in the salmon, potatoes, salt and pepper. Place the oil in a 10" ovenproof, non-stick skillet. Set over medium heat, and when hot, add the egg mixture. As the eggs begin to set on the bottom, gently move a heatproof spatula across the bottom and sides of the skillet to form large, soft curds that are still moist. Broil the top of the frittata until it is light golden brown. Let set a few minutes before carefully removing from the pan onto a cutting board. Cut into 6 wedges and plate them. Garnish the wedges of frittata with sour cream and green onion.