Instructions

1. Preheat the oven to 350°F (175°C).
2. In a large mixing bowl, whisk together 6 large eggs, 1/4 cup of milk, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper until well blended.
3. In a large oven-safe skillet, heat 2 tablespoons of olive oil over medium heat. Add 1 finely chopped onion and sauté for about 5 minutes until softened.
4. Add 2 cups of fresh spinach to the skillet and cook until wilted, about 3 minutes. If using frozen spinach, ensure it's thawed and drained before adding.
5. Stir in 1/2 cup of crumbled feta cheese and 1/4 cup of chopped Kalamata olives into the spinach mixture.
6. Pour the egg mixture over the spinach, onion, and cheese. Cook for about 5 minutes on the stovetop until the edges begin to set.
7. Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the frittata is golden and set in the center.
8. Remove from the oven, let cool for a few minutes, then slice into wedges and serve warm or at room temperature.