01 - In a medium bowl, whisk together the eggs, milk, salt, pepper, and nutmeg until fully combined.
02 - Heat butter in a nonstick skillet over medium heat. Add the shallot (if using) and sauté for 1 minute until fragrant.
03 - Add the spinach and cook, stirring, for 1–2 minutes until wilted.
04 - Pour the egg mixture over the spinach in the skillet. Let cook undisturbed for 1–2 minutes until the edges begin to set.
05 - Gently lift the edges with a spatula, allowing uncooked egg to flow underneath. Cook for another 1–2 minutes until almost set.
06 - Sprinkle the crumbled feta evenly over one half of the omelet.
07 - Using the spatula, fold the omelet in half and cook for 1 more minute, allowing the feta to warm through.
08 - Slide onto a plate and serve immediately.