Preheat oven to 400°F. Lightly spray a 2-quart (8x8-inch) casserole dish with nonstick spray and set aside.
Chop the broccoli (crowns and stems) into bite-sized pieces. Bring a large pot of water to a boil, then add the broccoli. Boil for 2-3 minutes, until tender-crisp. Drain well.
1 pound fresh broccoli
In a large bowl, combine the soup, ½ cup Monterey jack cheese, cheddar cheese, milk, sour cream, mustard, garlic powder, and pepper. Whisk well to combine.
10.5 ounces condensed cream of chicken soup, 1 cup shredded Monterey jack cheese, ½ cup shredded cheddar cheese, ⅓ cup milk, ⅓ cup sour cream, 1 teaspoon whole grain mustard, ½ teaspoon garlic powder, ½ teaspoon ground black pepper
Gently stir in the steamed broccoli and chicken to coat. Transfer the mixture to the prepared casserole dish. Sprinkle on the remaining cheese.
2½ cups cubed cooked chicken
In a small bowl, combine the breadcrumbs and melted butter and stir. Sprinkle the topping over the casserole.
¼ cup breadcrumbs, 2 tablespoons unsalted butter
Bake for 15-20 minutes, or until the casserole is bubbly and the topping is lightly browned.
Serve as is, or over rice, noodles, or mashed potatoes.
Notes
Easily double this recipe and bake it in a 4-quart baking dish (9x13-inches) to feed 8 people! Bake for an additional 10-15 minutes.
Storage: Store chicken divan casserole in an airtight container in the refrigerator for up to 3 days or in the freezer for up to 3 months.