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