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1
Cut top third of each asparagus stalk diagonally into 1/2-inch-thick slices, reserving tips and slices together, then coarsely chop remainder. Bring water (5 1/2 cups) and 1/2 teaspoon salt to a boil in a 3- to 4-quart saucepan, then add chopped asparagus and cook, uncovered, until very tender, 6 to 7 minutes. Transfer with a slotted spoon to a food processor (not a blender, which would require adding liquid).
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2
Add reserved asparagus tips and slices to boiling water and cook, uncovered, until crisp-tender, 2 to 3 minutes. Transfer with slotted spoon to a sieve, reserving cooking liquid in pan, and rinse under cold water to stop cooking. Drain well and reserve in another bowl.
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3
Measure cooking liquid and, if necessary, add enough water to bring total to 4 cups, then reserve.
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4
Cook onion with pepper and 1/4 teaspoon salt in oil in a 4- to 5-quart heavy pot over moderate heat, stirring occasionally, until softened, 5 to 7 minutes. Add barley and cook, stirring, 1 minute.
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5
Add wine and boil, stirring, until liquid is absorbed, about 1 minute.
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6
Add 4 cups reserved asparagus-cooking liquid and bring to a boil, covered, then reduce heat and simmer, covered, until barley is tender (it should be chewy) and mixture is thickened to a stewlike consistency, 35 to 40 minutes.
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7
Meanwhile, mince garlic and mash to a paste with remaining 1/4 teaspoon salt using side of a large heavy knife, then add to asparagus in food processor along with zest and puree until smooth.
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8
When barley is cooked, stir in asparagus puree, asparagus-tip mixture, and enough additional water to thin to desired consistency and cook over moderate heat, stirring, until hot, about 1 minute. Stir in cheese, then season with salt and pepper. Serve with hazelnuts and additional cheese on the side.
