In a medium bowl, beat 3 large eggs, 2 tablespoons water and a pinch salt and pepper with a fork. Mix in 1 teaspoon chopped chives or other herb (optional). In an 8-inch nonstick skillet, melt 1 1/2 teaspoons unsalted butter over medium-high heat and pour in the egg mixture. Stir constantly with a rubber spatula, scraping the bottom of the pan, until the eggs are about two-thirds cooked, about 1 minute. Turn the heat to very low and spread the mixture evenly. Sprinkle 1/2 cup finely shredded gruyere cheese on top. When the bottom of the omelet is set, fold it in half to enclose. Serve with buttered toast.