- 2 medium
- baking potatoes, peeled and cut into 1/4 inch thick slices (about 3 cups)
- 2 medium
- sweet potatoes, peeled and cut into 1/4 inch thick slices (about 4 cups)
- 2 qt
- low sodium chicken stock
- 2 Tbsp
- canola oil
- 3 Tbsp
- all-purpose flour
- 2 clove
- garlic, crushed
- 1 1/2 c
- 2 sprig(s)
- 3/4 tsp
- kosher salt, divided
- 1/4 tsp
- black pepper, freshly ground
- 3 oz
- gruyere cheese, shredded (about 3/4 cup)
- cooking spray
- 2 Tbsp
- fresh chives, chopped, divided
- 1 1/2 tsp
- fresh thyme, chopped
- 1 oz
- fresh parmigiano-reggiano cheese, grated (about 1/4 cup)
How to Make Two-Potato Gratin
- 1Preheat oven to 350 degrees.
- 2Place potatoes in a large stockpot; cover with stock. Bring the mixture to a boil. Cook 4 minutes. Remove from heat. Carefully remove the potatoes from the pot using a slotted spoon, reserving the cooking liquid. Arrange the potato slices in a single layer on a jelly-roll pan; set aside.
- 3Strain the cooking liquid through a fine mesh sieve over a bowl; reserve 1 cup cooking liquid. Discard the solids and the remaining cooking liquid.
- 4Heat a medium saucepan over medium heat. Add the oil to the pan. Sprinkle the flour over the oil; cook 1 minute, stirring constantly with a whisk. Add the garlic; cook 2 minutes, stirring frequently. Combine milk and reserved 1 cup cooking liquid. Gradually pour milk mixture into the flour mixture in pan, stirring constantly with a whisk. Add thyme sprigs to the pan. Bring mixture to a boil; cook 4 minutes or until slightly thick, stirring frequently. Remove from the heat. Strain mixture through a fine-mesh sieve over a bowl, reserving sauce; discard solids. Stir 1/2 teaspoon salt, pepper, and Gruyere cheese into the sauce.
- 5Spread 1/2 cup sauce in the bottom of a broiler-safe 2 quart ceramic baking dish coated with cooking spray. Arrange a single, flat layer of sweet potato and then baking potato slices over the sauce. Over the flat layer, alternate baking potato and sweet potato slices, in shingle-like fashion. Sprinkle evenly with remaining 1/4 teaspoon salt, 1 tablespoon chives, and shopped thyme; pour remaining sauce over the potato mixture. Sprinkle with Parmigiano-Reggiano cheese. Bake at 350 degrees for 1 hour or until the potatoes are tender when pierced with a knife.
- 6Remove gratin from the oven. Preheat the broiler to high.
- 7Place the gratin in the oven. Broil the gratin 3 minutes or until lightly browned. Sprinkle with the remaining 1 tablespoon chives.