Preheat your oven to 375°F.
Grease a large baking dish to prevent sticking.
In a large pot, bring lightly salted water to a boil.
Add broccoli and cook for about 5 minutes until tender.
Drain and set aside.
In a separate saucepan, melt 1/4 cup butter over medium heat.
Whisk in the flour, cooking until the mixture is smooth and free of lumps.
Gradually add milk while stirring constantly, until the sauce is thickened.
Stir in cheddar and Parmesan cheeses until melted and smooth.
Season with salt and pepper.
Arrange the cooked broccoli in the prepared baking dish.
Pour the cheese sauce over the broccoli, spreading it evenly.
Combine breadcrumbs with 1 tsp of melted butter.
Sprinkle the breadcrumb mixture over the cheese sauce.
Bake in the preheated oven for 20-25 minutes, until the top is golden brown and bubbly.