Preheat your oven to 375°F (190°C).

In a skillet, heat olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.

Add the chopped spinach to the skillet and cook until wilted, about 2 minutes. Remove from heat and let cool slightly.

In a mixing bowl, whisk together eggs, milk, salt, and pepper. Stir in the cooled spinach and onion mixture, along with the crumbled feta cheese.

Roll out your pie crust or phyllo dough and cut it into small circles to fit into muffin tins, pressing them into the bottom.

Pour the egg mixture into each crust, filling them about 3/4 full.

Bake for 20-25 minutes or until the egg is set and the tops are lightly golden.

Let cool for a few minutes before removing from the muffin tin. Serve warm.