01 - Preheat oven to 350°F (180°C) and lightly grease a medium baking dish.
02 - Steam or blanch broccoli florets and carrot slices for 3 to 4 minutes until just tender. Drain well and set aside.
03 - In a medium saucepan over medium heat, melt butter. Whisk in flour and cook for 1 minute, stirring constantly.
04 - Gradually whisk in milk until mixture is smooth and thickened. Remove from heat. Stir in shredded cheddar, garlic powder, onion powder, salt, and pepper until cheese melts and sauce is creamy.
05 - Fold broccoli and carrots into the cheese sauce, coating evenly. Spoon mixture into the prepared baking dish.
06 - In a mixing bowl, combine panko breadcrumbs, melted butter, and Parmesan cheese if using. Sprinkle evenly across the casserole surface.
07 - Bake uncovered for 25 to 30 minutes, until top is golden brown and bubbling. Allow to rest for 5 minutes before serving.