Crack eggs into a bowl, whisk to combine and set aside.
Heat butter in a cast-iron skillet or heavy bottom pan on medium-high heat.
Once the butter has melted, add the chopped spinach and a pinch of salt and cook, stirring often, until the spinach is wilted, tender and bright green, about 1 to 2 minutes.
Once the spinach has cooked, reduce the heat to medium, add whisked eggs to the pan and, using a spatula, gently stir and fold the eggs. When eggs are about 1⁄2 way cooked, add crumbled feta cheese to continue folding and stirring eggs until cooked to your liking.
Once cooked, remove from the pan, season with additional salt and pepper to taste, and serve immediately.