"Caramelized onions add a touch of sweetness to a classic potato gratin. Though Comté, a nutty and complex French cheese made in the Jura Mountains, is worth seeking out, Gruyère from neighboring Switzerland makes a good substitute...."
INGREDIENTS
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2 Tbs. unsalted butter
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1 Tbs. extra-virgin olive oil
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1 lb. yellow onions, thinly sliced (about 3-1/2 cups)
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Kosher salt and freshly ground black pepper
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2 lb. Yukon Gold potatoes (about 5 large)
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1-1/2 tsp. chopped fresh thyme
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4 oz. grated Comté cheese (about 1-1/2 cups)
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2 cups whole milk
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Pinch freshly grated nutmeg