01 -
Preheat oven to 175°C and grease a 2.5-quart casserole dish with cooking spray.
02 -
In a large saucepan, melt half the butter over medium heat. Add sliced shallots and chopped garlic, cooking and stirring occasionally until softened, about 3 to 5 minutes, taking care to avoid browning.
03 -
Whisk in all-purpose flour with the shallots and garlic; cook for 1 to 2 minutes until the mixture becomes lightly golden and fragrant, stirring constantly to eliminate raw flour taste.
04 -
Gradually add whole milk, half-and-half, kosher salt, and black pepper while whisking continuously. Reduce heat to low and simmer, stirring frequently, until the sauce thickens slightly, about 3 to 5 minutes.
05 -
Remove the saucepan from heat and stir in 3 cups (approximately 330 g) of shredded sharp cheddar cheese until fully melted and smooth.
06 -
Place broccoli florets evenly in the prepared dish. Pour the cheese sauce over the broccoli, spreading to cover completely.
07 -
In a small bowl, combine remaining 1 cup (about 110 g) shredded cheddar cheese with panko bread crumbs. Sprinkle this mixture evenly over the casserole.
08 -
Cover the casserole with foil or a lid and bake for 20 minutes in the preheated oven.
09 -
Remove the cover and bake an additional 10 to 15 minutes, or until the topping is golden brown and bubbly. Serve warm.