There is something grounding about the rhythm of making a frittata. It begins with the soft sizzle of onions hitting a hot pan, followed by the vibrant pop of fresh green spinach wilting into emerald silk. It is a dish that respects the ingredient. Unlike a complicated soufflé that demands constant attention, the frittata is forgiving and hearty, welcoming your input and rewarding you with a golden-brown finish every single time.

I often turn to this recipe when my kitchen feels bare, yet I crave something substantial. It is the ultimate "clean-out-the-fridge" meal, but it feels elegant enough to serve at a weekend brunch. When you slice into it, you want to see that distinct separation of fluffy egg and pockets of sharp, salty feta, all held together by the earthy sweetness of sautéed onions. It’s simple, simple cooking.

To capture the best flavor, try to source quality eggs. You will notice the difference in the richness of the yolk and the final structure of the dish.

• 8 large pasture-raised eggs
• 4 cups fresh baby spinach, packed
• 1/2 cup high-quality crumbled feta cheese
• 1 medium yellow onion, finely diced
• 2 tbsp extra-virgin olive oil
• 1/4 cup whole milk or plain Greek yogurt (for added creaminess)
• 1/2 tsp sea salt (adjust to taste, considering the feta is salty)
• 1/2 tsp freshly cracked black pepper
• Optional: 1/4 tsp red pepper flakes for a subtle warmth

Precision in the initial steps ensures the perfect texture throughout the dish.

1. Prep the Base: Preheat your oven to 375°F (190°C). While the oven warms, grab your 10-inch oven-safe skillet—a seasoned cast iron is ideal here for its steady heat retention.
2. Sauté the Aromatics: Heat the olive oil over medium heat. Toss in the onions and sauté until they are soft, translucent, and just beginning to turn golden at the edges. This sweetness is the foundation of the dish.
3. Wilt the Greens: Add the baby spinach to the pan. Use tongs to toss it until it wilts completely. Important: If you see excess moisture gathering in the pan, drain it carefully. Watery spinach is the enemy of a firm frittata.
4. The Whisking Ritual: In a medium bowl, whisk the eggs, milk (or yogurt), salt, pepper, and red pepper flakes vigorously. You want to see small bubbles on the surface; this air incorporation ensures the eggs lift beautifully as they bake.
5. The Merge: Pour the egg mixture over the spinach and onions. Sprinkle the crumbled feta evenly across the top. Let it sit on the stovetop, undisturbed, for about 3 minutes. You are looking for the edges to set while the center remains slightly loose.
6. The Finish: Move the skillet carefully into your preheated oven. Bake for 10–12 minutes. The center should be set, and the top should be puffed and golden.

This dish is fantastic for meal prep because it holds its texture remarkably well. Let the frittata cool completely before covering it. It will keep in an airtight container in your refrigerator for up to 3 days. To reheat, I suggest the oven or a toaster oven rather than the microwave—a quick 5–8 minutes at 350°F will bring back that just-baked fluffiness without the "rubbery" texture that often occurs in high-heat microwaves.