Step 1

Preheat the oven to 350°F. Bring a large pot of salted water to a boil over high heat. Add the macaroni and cook until tender but still firm to the bite, stirring occasionally, 8 to 10 minutes. Drain.

Step 2

Heat the olive oil in a large skillet over medium heat. Add the mushrooms, onion, and garlic. Cook, stirring, until the mushrooms are tender and the onion is golden, about 7 minutes. Stir in the tomatoes, spinach, and red pepper flakes and cook until heated through, about 5 minutes.

Step 3

In a small bowl, mix together the bread crumbs, ¼ cup of the Parmesan cheese, and ¼ cup of the Romano cheese. Spread a 9 x 13 x 2-inch glass baking dish with the softened butter and sprinkle half of the bread crumb mixture inside the dish to coat.

Step 4

In a large bowl, combine the vegetable mixture with the cooked macaroni, cubed mozzarella, the remaining Parmesan and Romano cheeses, and the nutmeg. Spoon into the baking dish and top with the remaining bread crumb mixture. Dot the top with the 2 tablespoons of cold butter and bake until the top is golden brown, 30 to 40 minutes.