Preheat oven to 350℉. Grease a 9x13 casserole dish and set aside.
Bring a pot of water to a boil. Add broccoli florets and boil for about 3 minutes, or until broccoli is tender crisp and bright green. Drain and set aside to cool.
In a saucepan over medium heat, melt butter. Add flour and whisk to combine, creating a paste. Cook for one minute.
Add milk, salt, pepper, paprika, and garlic powder, whisking to combine. Cook for 3-4 minutes, whisking frequently, or until mixture thickens slightly. Remove from heat.
Add shredded cheese and stir until melted.
Add your cooled, par-cooked broccoli and stir until evenly coated. Pour into prepared casserole dish and spread into an even layer.
In a small bowl, add panko bread crumbs, melted butter, salt, and garlic powder. Toss until evenly incorporated. Sprinkle over casserole in an even layer.
Bake casserole, uncovered, for about 18-20 minutes, or until hot and bubbly in the center. Optionally, turn on the broiler for 2 minutes to brown the top.
Remove from oven and allow to stand for 5 minutes before serving.
