01 - Whisk together eggs, milk, salt, pepper, and nutmeg in bowl until fully combined and slightly frothy.
02 - Heat butter or oil in nonstick skillet over medium heat. Add shallot or onion, cook until translucent, about 1-2 minutes.
03 - Add chopped spinach to skillet, stir constantly until just wilted, approximately 1 minute. Spread evenly across pan bottom.
04 - Pour egg mixture over vegetables, tilting skillet to coat evenly. Cook undisturbed 2-3 minutes until edges begin to set.
05 - Gently lift cooked edges with spatula, tilting pan to let uncooked egg flow underneath. Repeat until mostly set but slightly moist on top.
06 - Sprinkle crumbled feta cheese evenly over one half of the omelet.
07 - Fold omelet in half over filling. Cook 30 seconds to melt cheese. Slide onto plate and serve immediately.