01 - Preheat oven to 350°F (180°C). Grease a medium baking dish.
02 - Steam or blanch 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 butter. Whisk in flour and cook for 1 minute, stirring constantly. Gradually add milk, whisking until thickened and smooth.
04 - Remove saucepan from heat. Add shredded cheddar cheese, garlic powder, onion powder, salt, and pepper. Stir until cheese is melted and sauce is creamy.
05 - Add cooked broccoli and carrots to the cheese sauce and gently fold to combine. Transfer mixture to the prepared baking dish.
06 - In a mixing bowl, mix panko breadcrumbs, melted butter, and grated Parmesan cheese if using. Sprinkle evenly over the vegetable mixture.
07 - Bake for 25 to 30 minutes, or until the top is golden brown and bubbling. Let rest for 5 minutes before serving.