01 - Whisk together eggs, milk, salt, black 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 diced shallot or onion and sauté until translucent and fragrant, approximately 1–2 minutes.
03 - Add chopped spinach to the skillet and cook, stirring frequently, until leaves are completely wilted, about 1 minute.
04 - Pour the egg mixture into the skillet, tilting the pan to spread evenly over the spinach and aromatics.
05 - Cook undisturbed for 2–3 minutes until edges begin to firm. Gently lift edges with a spatula, allowing any uncooked egg to flow underneath for even cooking.
06 - Sprinkle crumbled feta cheese evenly across one half of the omelet surface.
07 - When eggs are mostly set but the top remains slightly glossy, fold the omelet in half over the filling. Continue cooking for 30 seconds, then slide onto a serving plate.
08 - Serve immediately, optionally garnished with additional crumbled feta or fresh herbs.