Place the potatoes, onion, margarine and bouillon cube into a soup pot, and fill with enough water to cover the potatoes by 1 to 2 inches. Bring to a boil, and cook for 30 minutes, until potatoes are falling apart. You can smash them up a little if you prefer the texture. Drizzle the beaten eggs into the pot, while stirring constantly. Continue to cook and stir for about 2 minutes, until the eggs are completely cooked in long strands.