Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter or nonstick spray.

Cook the protein. In a skillet, cook the sausage or bacon until browned and crisp. Drain excess fat if needed and set aside.

Sauté the vegetables. In the same skillet, add olive oil or butter. Sauté onion and bell pepper with a pinch of salt for 3–4 minutes until softened. Add broccoli and cook 2–3 minutes more. Stir in garlic and spinach until the spinach just wilts. Remove from heat.

Whisk the eggs. In a large bowl, whisk together eggs, heavy cream, remaining salt, pepper, smoked paprika, and red pepper flakes until smooth and well combined.

Assemble the casserole. Spread the cooked sausage or bacon evenly in the prepared dish. Top with the sautéed veggies. Sprinkle half the cheese over the top.

Pour in the eggs. Slowly pour the egg mixture over the fillings, tilting the dish slightly as needed so it spreads evenly. Top with the remaining cheese.

Bake for 28–35 minutes, until the center is just set and the edges are lightly golden. A knife inserted near the center should come out clean, or the center should reach about 165°F (74°C).

Rest and serve. Let the casserole rest for 5–10 minutes to set. Slice into squares and garnish with chopped herbs if you like.