01 - Whisk together eggs, milk, salt, pepper, and nutmeg in a bowl until fully combined and uniform in color.
02 - Heat butter or olive oil in a nonstick skillet over medium heat. Add shallot or onion and cook until translucent, approximately 1-2 minutes.
03 - Add chopped spinach to skillet and stir continuously until leaves are completely wilted, about 1 minute.
04 - Pour egg mixture into skillet, tilting pan to spread eggs evenly over spinach and aromatics.
05 - Cook without disturbing for 2-3 minutes until edges begin to firm. Gently lift edges with spatula, allowing uncooked egg to flow underneath.
06 - Sprinkle crumbled feta cheese evenly over one half of the omelet.
07 - Fold omelet in half when eggs are mostly set but top remains slightly moist. Cook additional 30 seconds, then transfer to serving plate.
08 - Serve immediately, optionally garnished with additional feta crumbles or fresh herbs such as dill or parsley.