INGREDIENTS
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Ingredients
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2-1/2 tablespoons butter
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12 springs thyme
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1 large sweet onion, sliced into 1/4 inch plus slices
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3/4 to 1 pound waxy potatoes, peeled and sliced
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2 tablespoons oil
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1/2 cup Gruyere, grated
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1 cup mozzarella, grated
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sea salt and cracked black pepper