Preheat your oven to 375°F (190°C). Lightly grease a medium baking dish with butter or cooking spray.

Bring a large pot of salted water to a boil. Add the cauliflower florets and cook for about 5 minutes, just until tender but not mushy. Drain well and set aside.

In a saucepan, melt the butter over medium heat. Stir in the flour and whisk for 1–2 minutes to form a roux.

Gradually add the milk while whisking constantly, making sure no lumps remain. Continue cooking until the sauce thickens and coats the back of a spoon.

Stir in Dijon mustard, garlic powder, onion powder, salt, and pepper. Mix well.

Add 1½ cups of cheddar cheese and all of the mozzarella cheese to the sauce. Stir until smooth and melted.

Add the drained cauliflower into the cheese sauce and gently fold to coat evenly.

Transfer the mixture to the prepared baking dish. Sprinkle the remaining cheddar cheese, Parmesan cheese, and optional breadcrumbs on top.

Dust lightly with paprika if desired.

Bake uncovered for 25–30 minutes, or until the top is golden brown and bubbly.

Garnish with fresh parsley before serving.