01 -
Preheat oven to 350°F and heat a large pot of water. Boil or steam broccoli and cauliflower for 4-5 minutes until semi-tender, then drain and place in a lightly greased 9x13 inch pan.
02 -
In a large skillet, melt the butter over medium heat and cook onion and garlic until tender and fragrant, about 4-5 minutes. Whisk in the flour and cook briefly until thick. Gradually whisk in milk and chicken broth, continuing to whisk until the mixture is smooth and creamy. Season with salt, black pepper, and fresh thyme.
03 -
Pour the creamy sauce over the broccoli and cauliflower. Sprinkle shredded cheddar and parmesan cheese evenly on top.
04 -
In a small bowl, combine bread crumbs, garlic powder, and melted butter. Mix well and spread evenly over the casserole.
05 -
Bake in preheated oven at 350°F for 15-20 minutes until the topping is golden brown and the broccoli and cauliflower are tender.