1. Melt 2 tablespoons of the butter in large skillet on medium heat. Add onions; cook and stir 10 minutes or until golden. Add potatoes; cook and stir 5 minutes. Salt and pepper to taste.
2. Meanwhile, heat broth in small saucepan until hot. Remove from heat. Crumble saffron over broth. Let stand about 5 minutes or until saffron is softened.
3. Mix eggs, green onions, saffron mixture, salt and pepper in large bowl with wire whisk.
4. Heat remaining 2 tablespoons butter in large nonstick skillet on medium heat until hot. Add egg mixture, spreading to cover bottom of skillet. As egg mixture sets, lift slightly with spatula to allow uncooked portion to flow underneath. When egg mixture is set but top is still slightly moist, spoon potato mixture onto half of the omelet. Slip spatula underneath other half of omelet and tip skillet to loosen. Gently fold omelet in half. Slide onto serving platter.