INGREDIENTS
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1tablespoonunsalted butter
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1/2cupplus 2 tablespoons olive oil
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1/2large yellow onion, finely diced
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1teaspoonsugar
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1teaspoonkosher salt
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1/2cupsherry vinegar
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1/4teaspoonblack pepper
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2poundsgreen beans, trimmed
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2teaspoonsgrated orange zest