01 - Whisk together eggs, milk, salt, pepper, and nutmeg in a medium bowl until fully combined and uniform in color.
02 - Heat butter in a nonstick skillet over medium heat. Add diced shallot and sauté for 1 minute until fragrant and translucent.
03 - Add chopped spinach to the skillet and cook, stirring constantly, for 1–2 minutes until completely wilted and reduced in volume.
04 - Pour the egg mixture evenly over the spinach. Let cook undisturbed for 1–2 minutes until the edges begin to set and pull away from the pan.
05 - Gently lift the edges with a spatula, tilting the pan to allow uncooked egg to flow underneath. Continue cooking for another 1–2 minutes until almost set but still slightly glossy on top.
06 - Sprinkle crumbled feta cheese evenly over one half of the omelet, leaving about 1/2 inch border from the edge.
07 - Using the spatula, carefully fold the unfilled half over the feta. Cook for 1 additional minute until the feta warms through and the omelet is fully set.
08 - Slide the omelet onto a warm plate and serve immediately while hot.