01 - Preheat oven to 350°F (180°C). Lightly grease a medium baking dish.
02 - Steam or blanch broccoli florets and sliced carrots for 3–4 minutes until just tender. Drain thoroughly and set aside.
03 - In a medium saucepan over medium heat, melt 2 tablespoons of butter. Whisk in flour and cook for 1 minute, stirring constantly. Gradually add milk, whisking until the mixture is smooth and starts to thicken.
04 - Remove saucepan from heat and stir in shredded cheddar cheese, garlic powder, onion powder, salt, and pepper. Mix until the cheese is fully melted and sauce is creamy.
05 - Gently fold the blanched broccoli and carrots into the cheese sauce. Transfer the entire mixture into the prepared baking dish, spreading evenly.
06 - In a mixing bowl, combine panko breadcrumbs, melted butter, and grated Parmesan cheese if using. Evenly sprinkle the topping over the vegetable mixture.
07 - Bake for 25–30 minutes or until the topping is golden brown and the casserole is bubbling. Allow to rest for 5 minutes before serving.