01 - Preheat oven to 350°F (180°C) and lightly grease a medium-sized baking dish.
02 - Steam or blanch broccoli florets and sliced carrots for 3 to 4 minutes until just tender. Drain vegetables and set aside.
03 - Melt 2 tablespoons butter in a medium saucepan over medium heat. Whisk in flour and cook for 1 minute, stirring constantly. Gradually add milk, whisking until smooth and thickened.
04 - Remove saucepan from heat. Stir in shredded cheddar, garlic powder, onion powder, salt, and black pepper. Mix until cheese is fully melted and sauce is creamy.
05 - Gently fold cooked broccoli and carrots into the cheese sauce, ensuring all pieces are evenly coated. Transfer vegetable mixture to prepared baking dish.
06 - In a small mixing bowl, combine panko breadcrumbs, melted butter, and grated Parmesan cheese if using. Sprinkle topping mixture evenly over casserole.
07 - Bake for 25 to 30 minutes until topping is golden brown and cheese is bubbling. Allow to rest for 5 minutes before serving.