INGREDIENTS
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2 tablespoons vegetable oil
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2 large onions, thinly sliced
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1/4 small onion, finely chopped
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1 pound ground beef chuck (20% fat)
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1 tablespoon ketchup
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1/2 teaspoon garlic powder
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1 teaspoon kosher salt
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1/4 teaspoon freshly ground black pepper
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1 tablespoon vegetable oil
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8 slices seeded rye bread (preferably Levy’s)
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4 ounces aged sharp cheddar, thinly sliced
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4 ounces Swiss cheese (such as Emmenthal), thinly sliced
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8 teaspoons mayonnaise