Step 1

Preheat the oven to 450 degrees F°

Step 2

Pretreat a large baking dish with one tablespoon of butter and add the broccoli, cauliflower carrots, and onion. Roast until slightly golden browned, about 15 minutes.

Step 3

In a medium saucepan, melt four tablespoons of butter, whisk in the flour and let it cook over medium heat for 3 minutes. Turn the heat off, whisk in the half-and-half, then turn the heat up to high and keep whisking to avoid the flour from clumping. Add the Cheddar cheese, kosher salt, pepper, nutmeg, and whisk until the cheese is melted.

Step 4

Remove the broccoli, cauliflower, carrots, and onion from the oven and pour the Cheddar cheese mixture over the top. Sprinkle evenly with the parmesan cheese and bake until golden brown on 400 degrees F, 25 to 30 minutes.

Step 5

Serve after cooling the casserole for about 5 minutes on a heat-safe area