01 - Preheat the oven to 350°F. Lightly grease a medium-sized baking dish.
02 - Steam or blanch the broccoli florets and carrot slices for 3 to 4 minutes until just tender. Drain thoroughly and set aside.
03 - In a medium saucepan over medium heat, melt the butter. Whisk in the flour and cook for 1 minute until foaming, without letting it brown. Gradually add the milk, whisking constantly until the mixture is smooth and slightly thickened.
04 - Remove from heat. Stir in the shredded cheddar cheese, garlic powder, onion powder, salt, and pepper. Mix until the cheese is melted and the sauce is creamy.
05 - Gently fold the cooked broccoli and carrots into the cheese sauce, ensuring the vegetables are well coated. Transfer the mixture to the prepared baking dish, spreading it evenly.
06 - In a small mixing bowl, combine the panko breadcrumbs, melted butter, and Parmesan cheese, if using. Sprinkle the topping evenly over the vegetable and cheese mixture.
07 - Bake for 25 to 30 minutes, or until the top is golden brown and bubbling. Let stand for 5 minutes before serving.