Best ever cauliflower cheese

Ingredients: 1 large cauliflower, cut into florets 2 tablespoons butter 2 tablespoons all-purpose flour 2 cups milk 1 cup grated cheddar cheese 1 teaspoon Dijon mustard 1 teaspoon garlic powder Salt and pepper to taste 1/4 cup grated Parmesan cheese 1/4 cup breadcrumbs (optional)