Serves 6

Perfect as a side with just about any roast or steak, this old-fashioned, rich, steakhouse classic will delight guests. Cooking spinach can be tricky since it won’t all fit into most skillets. Work in batches until it is all fully wilted. Then wring out the excess water so that the finished gratin is not too soupy. Cook the mushrooms, stir together a roux-based cream sauce and bake until the filling bubbles and the breadcrumbs are golden.

Butter (for the dish)

2 tablespoons olive oil

3 cloves garlic, sliced

20 ounces baby spinach

1 pound button mushrooms, sliced

Salt and pepper, to taste

4 tablespoons butter

1 onion, chopped

3 tablespoons flour

1 teaspoon dry mustard

¼ teaspoon ground nutmeg

½ cup white wine

1½ cup heavy cream

½ cup shredded white cheddar

½ cup grated Parmesan

¼ cup plain white breadcrumbs

1. Set the oven at 450 degrees. Generously butter a 10- to 12-inch shallow, oval gratin dish.

2. In a very large skillet over medium-high heat, heat 1 tablespoon of the olive oil. Add the garlic and cook, stirring, for 1 minute. Add half the spinach. Cook, stirring often, until it has wilted enough to make room in the pan for more spinach. Add the remaining spinach and cook, stirring often, for 8 to 10 minutes, or until it is all completely wilted. Tip the mixture into a colander. Wipe out the skillet.

3. Return the skillet to medium-high heat. Add the remaining 1 tablespoon olive oil. Stir in the mushrooms, salt, and pepper. Cook, stirring often, for 10 to 12 minutes, or until the mushrooms release their moisture and brown. Transfer to a large bowl.

4. In a saucepan over medium heat, melt the 4 tablespoons butter. Add the onion and cook, stirring, for 5 minutes or until the onion softens but the butter does not brown. Stir in the flour and cook, stirring constantly, for 3 minutes. Stir in the mustard and nutmeg.

5. Stir in the wine and cook, stirring often, for 3 minutes. The mixture will be very thick.

6. Stir in the cream and cook, stirring, 3 minutes more. Add the cheddar and ¼ cup of the Parmesan. Remove from the heat and stir until the cheese is fully melted.

7. Using a wooden spoon or your hands, gently press the spinach in the colander to release excess water. Chop coarsely and transfer to the bowl with the mushrooms.

8. Stir the sauce into the spinach mixture. Transfer to the gratin dish. Sprinkle with breadcrumbs and the remaining ¼ cup Parmesan.

9. Bake the gratin for 15 minutes.

10. Turn on the broiler. Place gratin dish on a rack about 6 inches below the element. Broil, watching the dish carefully, for 2 to 3 minutes or until golden. Karoline Boehm Goodnick

Karoline Boehm Goodnick can be reached at kboehmgoodnick@gmail.com