In a small bowl, whisk together the eggs, milk (if using), salt, and pepper until fully combined and slightly frothy.

Chop the spinach and crumble the feta. Set aside.

Heat butter or olive oil in a nonstick skillet (8-inch works best) over medium-low heat.

Add the chopped spinach and sauté for 30–60 seconds, just until wilted.

Pour the egg mixture evenly over the spinach. Allow it to cook undisturbed for 2–3 minutes, until the edges begin to set.

Sprinkle the feta evenly across one half of the omelette.

Once the center is mostly set but still slightly soft, gently fold the omelette in half using a spatula.

Cook for another 1–2 minutes until fully set but still tender inside.

Slide onto a plate and garnish as desired. Serve immediately.