It seems counter-intuitive to cook a vegetable before you bake it in a casserole, but precooking broccoli makes a casserole more successful than using the vegetable raw. The freshest broccoli heads have the darkest color and tightly closed buds. Use cooked broccoli in egg-based timbales, cooked pasta dishes, cheesy gratins, and the classic chicken and broccoli Mornay casserole with mushroom sauce.
Blanching
Blanching broccoli by cooking it very quickly in a pot of salted water and then "shocking" it in a bowl of ice water to stop the cooking process gives you the best result for a casserole. Blanching allows the broccoli to retain its bright green color and cooks the vegetable enough so that your casserole won't get watery from raw broccoli. The result is a crisp-tender vegetable that cooks evenly and looks wonderful in the casserole.
Cooking
To blanch broccoli, peel off any tough ends of the stalks, rinse the broccoli thoroughly, and cut the florets into 1 1/2-inch pieces and the stalk into 3/4-inch pieces. A large pot of boiling water allows the broccoli to begin cooking immediately without the water needing to reach a second boil. Boil the pieces for 2 to 5 minutes, then drain them and plunge them into a large bowl of ice water.
Classic Casseroles
Both chicken divan -- named for an old New York City restaurant called Divan Parisien -- and chicken Mornay rely on a creamy sauce, shredded or cubed chicken breasts, and broccoli. For either recipe, use 1 head of broccoli for every 2 pounds of chicken, and a sauce made with flour, chicken stock, and milk or cream. Add cooked mushrooms for chicken Mornay or a few tablespoons of sherry for chicken divan, and bake the casseroles at 375 degrees Fahrenheit for about 35 minutes.
A Quick Variation
A creamy cheese such as cheddar, feta, goat, Parmesan or Swiss, pairs well with the strong flavor of broccoli. For a casserole that you assemble hot and cook in the broiler for just 2 minutes, combine cooked broccoli with sauteed mushrooms and top the mixture with a cheesy sauce and bread crumbs. One rich sauce combines 2 cups of cheddar cheese with a thickened white sauce, a small amount of cream cheese and 2 eggs.