A quick smoky roux rounds out the flavors of this comforting zucchini casserole featuring carrot, onion, and Cheddar baked under a golden brown, panko-encrusted top.
- 6 tablespoons butter, divided
- 2 tablespoons all-purpose flour
- 1 ½ cups whole milk
- 2 teaspoons chicken bouillon granules
- ½ teaspoon smoked paprika
- ¼ teaspoon dried thyme, crushed
- 3 large zucchini, cut into 1/4-inch rounds
- ¼ sweet onion (such as Vidalia®), sliced
- 1 large carrot, shredded
- 1 large egg, beaten
- 1 ½ cups shredded extra-sharp Cheddar cheese
- ⅓ cup panko bread crumbs, or to taste
- cooking spray
- Melt 3 tablespoons butter in a saucepan over medium heat until a pinch of flour sprinkled into the oil will just begin to bubble. Whisk in flour, stirring constantly until mixture becomes paste-like and light golden brown, about 5 minutes. Slowly add milk, stirring to avoid lumps. Continue stirring until a smooth, thick sauce is obtained, about 10 minutes more. Whisk in bouillon, paprika, and thyme. Remove from heat and let sauce cool.
- Preheat the oven to 350 degrees F (175 degrees C). Lightly butter a 9x13-inch casserole dish.
- Melt remaining 3 tablespoons butter in a skillet over medium-high heat. Add zucchini and onion; saute until softened, 12 to 15 minutes. Add carrot and continue cooking for 2 minutes. Remove from heat.
- Add egg to the cooled sauce; whisk rapidly until smooth. Add Cheddar cheese and mix to combine.
- Layer zucchini mixture evenly into the prepared casserole dish. Pour sauce over vegetables and give it a slight stir to moisten throughout. Sprinkle bread crumbs on top and spray lightly with cooking spray.
- Bake in the preheated oven until bread crumbs start to brown, 20 to 25 minutes. Broil until panko is nicely browned, 2 to 4 minutes more. Remove from oven and let sit for 10 to 15 minutes before serving.