Heat the broiler.

Heat the olive oil in an 8-inch omelet pan. Add the onion and potato. Cook about 5 minutes, or until the onion is soft and the edges of the potato begin to brown and crisp. Add the vegetable stock and allow the potatoes to steam over medium heat until they are soft and the liquid is cooked off about 10 minutes.

In a bowl, beat together the eggs, egg whites, and yogurt. Pour into the omelet pan. Top with the salmon. Cook for 4 or 5 minutes, or until the bottom of the frittata begins to set. Transfer the pan to the oven and broil for 3 or 4 minutes, or until lightly browned and fluffy. Sprinkle with fresh dill, if desired. Remove from pan and cut into 4 servings.