1/4 cup unsalted butter
1/2 cup flour
3 cups milk
1 cup chicken stock
1/2 teaspoon nutmeg
2 cups grated Parmesan
2 cups shredded sharp cheddar
4 cups cooked rotisserie chicken, shredded
6 cups raw broccoli florets
Preheat the oven to 350 degrees F.
Heat the butter in a heavy-bottomed pot over medium heat. Sprinkle in the flour, and whisk together. Cook for 1 minute, then begin drizzling in the milk, whisking constantly. When all of the milk is added, add the chicken stock. Continue to cook until the mixture is thick and bubbly, then remove from the heat.
Add the nutmeg, half the Parmesan, and half the cheddar to the sauce and whisk until smooth.
Toss the chicken, broccoli, and sauce together and pour into a baking dish. Sprinkle the remaining cheese over the top.
Cover the casserole and bake for 15 minutes, then remove the foil and bake for an additional 15 minutes, until bubbly.
Remove from the oven and serve.