Cauliflower Mac and Cheese

Name: Cauliflower Mac and Cheese
Ingredients: 2 medium heads cauliflower, cut in florets ( 8 – 10 cups); 1/2 cup unsalted butter; 3 cloves garlic, minced; 1/2 teaspoon dried thyme; 1/3 cup all-purpose flour; 3 cups 2% milk; 1 1/2 teaspoons kosher salt; 1 1/2 teaspoons dry mustard; 1 teaspoon hot sauce; 1/2 teaspoon ground black pepper; 1/8 teaspoon ground nutmeg; 1 cup Swiss cheese, shredded; 1 cup Sharp cheddar cheese, shredded; 1 cup Panko bread crumbs; 2 tablespoons unsalted butter, melted