• Preheat the oven to 350°F. Coat a 9-by-13-inch baking dish with cooking spray.

Cook the broccoli.

• If you have steam-in-the-bag frozen broccoli, cook it according to the package directions, then place it in the baking dish. If your broccoli needs to be cooked on the stovetop, use a skillet so you do not have to dirty another pan. In a large skillet, simmer ½ cup water over medium-high heat. Add the broccoli, cover, and return the water to a simmer. Cover and cook until tender, about 5 minutes. Drain the broccoli well and transfer it to the baking dish. Set aside.

Warm the turkey.

• Wipe out the skillet and return it to the stove. Melt 1 tablespoon of butter over medium heat. Add the turkey and cook until heated through. Transfer the turkey to the baking dish with the broccoli. Set aside.

Sauté the vegetables.

• In the same skillet, melt 2 tablespoons of butter. Add the onion and cook until softened. Add the mushrooms and cook until tender and browned, about 6 to 7 minutes.

Make the creamy sauce.

• Add the remaining 1 tablespoon of butter. Sprinkle the flour over the onion-and-mushroom mixture and stir for 2 minutes to cook the flour. Reduce the heat to low and slowly add the warm milk, stirring until thickened, about 8 minutes. Gradually add both cheeses, allowing each addition to melt before adding more. Stir in the Dijon mustard, salt, and pepper.

Assemble the casserole.

• Pour the sauce over the turkey and broccoli. Toss gently to distribute the sauce without breaking up the broccoli.

Add the crunchy topping.

• Combine the melted butter and panko breadcrumbs, stirring until the crumbs are moistened. Sprinkle the buttered crumbs over the top of the casserole.

Bake.

• Bake for 20 to 25 minutes, until golden and bubbly. Let the casserole cool for 15 minutes before serving.

Serve.

• Serve Turkey Divan on its own or over cooked egg noodles or rice, if desired.