Preheat the oven to 350 degrees F (175 degrees C).
Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add broccoli, cover, and steam until tender, 3 to 5 minutes.
Melt 5 tablespoons butter in a saucepan over medium-low heat. Add flour, stirring constantly to prevent browning. Slowly pour in milk, stirring constantly. Remove from heat; stir in Cheddar cheese, salt, pepper, garlic powder, and onion powder.
Drain broccoli and place in a casserole dish. Pour cheese sauce on top.
Bake in the preheated oven for about 15 minutes. Meanwhile, crush bread into crumbs. Saute in a skillet with the remaining 1 tablespoon butter until golden, 2 to 3 minutes.
Spread bread crumbs over the broccoli and continue baking until golden brown, about 5 minutes more.
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