Preheat your oven to 350°F. In a skillet, heat 1 teaspoon of olive oil over medium heat. Add the chopped shallots and sauté until they become translucent, about 3-4 minutes. Next, add the baby spinach and cook until wilted, roughly 2 minutes. Remove from heat and allow to cool slightly.
In a large mixing bowl, whisk together the 24 beaten eggs, 2 cups of 2% milk, and 1/2 cup of heavy cream. Add in the kosher salt and black pepper to taste.
Once the spinach and shallots have cooled, gently fold them into the egg mixture. Add the crumbled feta cheese, chopped scallions, and diced tomatoes. Mix everything together until well combined.
Lightly spray your 9x13-inch baking dish with olive oil spray. Pour the egg and vegetable mixture into the prepared dish, spreading it evenly.
Place the casserole in the preheated oven and bake for about 45-50 minutes or until the center is set and the top is lightly golden. A toothpick inserted into the center should come out clean.
Once baked, remove the casserole from the oven and let it cool for about 10 minutes before slicing. Serve warm, garnished with extra scallions if desired.
