01 - Preheat oven to 350°F (180°C). Lightly grease a medium baking dish.
02 - Steam or blanch broccoli florets and carrot slices for 3–4 minutes until just tender. Drain 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, continue stirring until mixture thickens and is smooth. Remove from heat and add cheddar cheese, garlic powder, onion powder, salt, and pepper. Stir until cheese has fully melted and sauce is creamy.
05 - Gently fold steamed broccoli and carrots into cheese sauce. Transfer mixture to prepared baking dish, spreading evenly.
06 - In a mixing bowl, combine panko breadcrumbs, melted butter, and Parmesan if using. Sprinkle evenly over the casserole.
07 - Bake for 25–30 minutes until topping is golden and casserole is bubbling. Let rest 5 minutes before serving.