Combine eggs and milk in a small mixing bowl; mix just until blended. Heat butter in a 10-inch omelet pan or heavy skillet over medium heat.
Pour egg mixture into skillet all at once. As mixture starts to cook, gently lift edges of omelet with a spatula; tilt pan to allow uncooked portion to flow underneath. Cook until set but not dry. Sprinkle with salt.
Combine parsley, chives, marjoram, and rosemary; sprinkle over half the omelet, reserving 1 teaspoon herbs. Fold opposite side of omelet over herbs; transfer to a warm serving platter. Garnish with reserved herbs, and serve immediately.