Two-Potato Gratin

This recipe comes from the December 2012 issue of Cooking Light magazine. I love that it’s possible to have some wonderful comfort food without having to consume a huge amount of calories.

Two-Potato Gratin

2 medium baking potatoes, peeled and cut into ¼-inch-thick slices (about 3 cups)
2 medium sweet potatoes, peeled and cut into ¼-inch-thick slices (about 4 cups)
2 quarts no-salt-added chicken stock (such as Swanson)
2 tablespoons canola oil
3 tablespoons all-purpose flour
2 garlic cloves, crushed
1 ½ cups 2% reduced-fat milk
2 thyme sprigs
¾ teaspoon kosher salt, divided
¼ teaspoon freshly ground black pepper
3 oz. aged Gruyere cheese, shredded (about ¾ cup)
Cooking spray
2 tablespoons chopped fresh thyme
1 oz. fresh Parmigiano-Reggiano cheese, grated (about ¼ cup)

Preheat oven to 350 degrees.

Place potatoes in a large stock pot; cover with stock. Bring mixture to a boil; cool 4 minutes. Remove from heat. Carefully remove potatoes from pot using a slotted spoon, reserving cooking liquid. Arrange potato slices in a single layer on a jelly-roll pan; set aside. Strain cooking liquid through a fine-mesh sieve over a bowl; reserve 1 cup cooking liquid. Discard solids and remaining cooking liquid.

Heat a medium saucepan over medium heat. Add oil to pan. Sprinkle flour over oil; cook 1 minute, stirring constantly with a whisk. Add garlic; cook 2 minutes, stirring frequently. Combine milk and 1 cup reserved cooking liquid. Gradually pour milk mixture into flour mixture in pan, stirring constantly with a whisk. Add thyme springs to pan. Bring mixture to a boil; cook 4 minutes or until slightly thick, stirring frequently. Remove from heat. Strain mixture through a fine-mesh sieve over a bowl, reserving sauce; discard solids. Stir ½ teaspoon salt, pepper and Gruyere cheese into sauce.

Spread ½ cup sauce in bottom of a broiler-safe 1-quart ceramic baking dish coated with cooking spray. Arrange a single, flat layer of sweet potato and then baking potato slices over sauce. Over flat layer, alternate baking potato and sweet potato slices, in shingle-like fashion. Sprinkle evenly with remaining ¼ teaspoon salt, 1 tablespoon chives, and chopped thyme; pour remaining sauce over potato mixture. Sprinkle with Parmigiano-Reggiano cheese. Bake at 350 degrees for 1 hour or until potatoes are tender when pierced with a knife.

Remove gratin from oven. Preheat broiler to high.

Place gratin in oven. Broil gratin 3 minutes or until browned. Sprinkle with remaining 1 tablespoon chives.

Makes 8 servings, at 218 calories per