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1
Put all beef ingredients in a 5- to 6-quart heavy pot with 1 teaspoon salt and enough water (about 2 quarts) to cover beef. Simmer, partially covered, skimming foam and adding more hot water if necessary to keep beef covered, until tender, about 2 hours.
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2
Remove beef and shred (once cool).
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3
Strain broth through a fine-mesh sieve into a bowl, discarding solids, and skim off fat.
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4
Preheat broiler.
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5
Toss tomatoes with 1 tablespoons oil in a 4-sided sheet pan. Broil 3 to 4 inches from heat until softened and charred, 10 to 12 minutes.
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6
Slit guajillo chiles lengthwise, then stem and seed. Heat a dry heavy medium skillet (not nonstick) over medium heat until hot, then toast chiles in 2 batches, opened flat, turning and pressing with tongs, until more pliable and slightly changed in color, about 30 seconds per batch. Transfer to a bowl and soak in hot water to cover until softened, 20 to 30 minutes.
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7
Toast peppercorns, cumin seeds, allspice, and clove in hot skillet over medium heat, stirring constantly, until fragrant and a shade darker, 30 seconds to 1 minute. Transfer to a blender.
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8
Drain soaked chiles and puree in blender with toasted spices, broiled tomatoes, onion, garlic, 3
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9
, 2 cups broth, and 1 teaspoon salt until smooth, about 2 minutes. For a spicier sauce, add remaining 2
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10
and puree again.
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11
Heat remaining 2 tablespoons oil in cleaned pot over medium-high heat until it shimmers, then slowly add sauce, stirring (it will spatter), and simmer, stirring frequently, 5 minutes. Add beef and 1 cup broth (reserve remainder for another use) and cook over medium-low heat, stirring, until meat is heated through, about 5 minutes.
