Preheat the oven to 375°F (190°C).

Cook the pasta according to package instructions until al dente. Add the broccoli florets to the boiling pasta water during the last 2 minutes of cooking. Drain and set aside.

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and cook until translucent, about 5 minutes. Add the minced garlic and cook for another minute.

Sprinkle the flour over the onions and garlic, stirring continuously for 2 minutes to create a roux.

Slowly whisk in the milk and heavy cream, making sure there are no lumps. Continue cooking and stirring until the sauce thickens, about 5-7 minutes.

Add the dried basil, dried oregano, salt, and pepper to the sauce. Stir in the Parmesan cheese until melted and well combined.

Combine the cooked pasta and broccoli with the sauce, mixing until everything is evenly coated.

Transfer the mixture into a greased baking dish. Sprinkle the shredded mozzarella cheese evenly over the top.

In a small bowl, combine the breadcrumbs with melted butter and sprinkle over the mozzarella cheese.

Bake in the preheated oven for 20-25 minutes, or until the top is golden brown and the casserole is bubbly.

Allow to cool for a few minutes before serving.