Over medium heat, melt the butter using a non-stick pan.

Add the garlic and saute until fragrant.

Add the white onions and cook until translucent.

Pour the heavy whipping cream.

Add the cornstarch.

Add the broccoli florets.

Add water if the sauce is too thick.

Season it with salt and pepper.

Add the parmesan cheese.

Lastly, add the mozzarella cheese. Stir the mixture until well combined and the sauce is thick and creamy. Serve.