INGREDIENTS
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2 tablespoons olive oil
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1 large onion, thinly sliced (about 3 cups)
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2 chipotle peppers in adobo, finely chopped
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2 cloves garlic, minced
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Kosher salt and freshly ground black pepper
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1 1/2 pounds ground beef
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4 ounces pepper jack cheese, cut into 12 equal pieces
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1/4 cup ketchup
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1 tablespoon balsamic vinegar
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12 slider-size potato buns, split and toasted