01 - Whisk eggs, milk, salt, pepper, and nutmeg in bowl until fully blended.
02 - Heat butter in nonstick skillet over medium heat. Cook shallot 1–2 minutes until translucent.
03 - Add chopped spinach to skillet, stir constantly until wilted, about 1 minute.
04 - Pour egg mixture into skillet, tilt pan to spread evenly across vegetables.
05 - Cook 2–3 minutes undisturbed until edges set. Lift edges with spatula to let uncooked egg flow underneath.
06 - Sprinkle crumbled feta cheese over half the omelet surface.
07 - Fold omelet in half when eggs are mostly set but top remains slightly runny. Cook 30 seconds more.
08 - Slide omelet onto plate. Serve immediately with additional feta or fresh herbs if desired.