Preheat and prep: Heat the oven to 350°F (175°C). Grease an 8x8-inch or 9x9-inch baking dish with cooking spray or butter.
Sauté aromatics: Warm the olive oil or butter in a skillet over medium heat.
Add the onion with a pinch of salt and cook until soft, about 4–5 minutes. Stir in the garlic and cook 30 seconds.
Cook the spinach: Add the chopped spinach to the skillet. Cook just until wilted and any excess moisture cooks off, 1–2 minutes.
If using frozen spinach, make sure it’s very dry before adding.
Whisk the base: In a large bowl, whisk the eggs, milk, salt, pepper, and paprika or chili flakes if using.
Add the cheeses: Stir in the cottage cheese and half of the shredded cheese. Fold in the cooked spinach mixture and herbs, if using.
Assemble: Pour the mixture into the prepared baking dish. Sprinkle the remaining shredded cheese evenly over the top.
Bake: Place in the oven and bake for 28–35 minutes, until the center is set and the top is lightly golden.
A knife inserted in the center should come out clean.
Rest and serve: Let it rest for 5–10 minutes before slicing. This helps it set and slice cleanly.