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In a medium saucepan, bring broth to a simmer; remove from heat and cover to keep warm.
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Meanwhile, in a second medium, heavy bottomed saucepan, heat oil over medium heat. Add onion and barley; stir to combine. Reduce heat to low and cook, stirring occasionally, until onion is softened and barley is lightly toasted, about 5 minutes.
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Add a third of the broth, bring barely to a simmer, and cook over low heat, stirring occasionally until brother is almost absorbed, about 12 minutes.
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Repeat with next third of broth, and then with the final third. Remove pan from the heat and sit in the Parmesan, salt, and pepper to taste.