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1
Cook and stir bread crumbs with 2 tablespoons olive oil in a skillet over medium heat until bread crumbs are crispy and toasted, 2 to 5 minutes. Transfer breadcrumbs to a bowl to cool.
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2
Grind saffron threads with a mortar and pestle; pour white wine into mortar and stir to combine.
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3
Bring a large pot of lightly salted water to a boil. Cook bucatini in boiling water, stirring occasionally until almost cooked through but firm to the bite, 10 to 11 minutes. Drain, reserving 1/2 cup of the pasta water.
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4
Heat remaining olive oil in large skillet over medium heat. Cook and stir onion and fennel with a pinch of salt in hot oil until onion is soft, about 10 minutes.
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5
Stir raisins, garlic, and anchovy fillet into onion mixture; cook and stir until heated through, about 1 minute.
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6
Pour saffron-wine into skillet; cook until wine is almost evaporated, about 2 minutes. Pour 1 ladleful reserved pasta water into skillet and bring to a simmer. Stir pine nuts and red pepper flakes into sauce; simmer until flavors combine and sauce is reduced, about 5 minutes.
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7
Stir bucatini and sardines into wine mixture; increase heat to high, and cook, stirring frequently and adding more reserved pasta water as necessary, until sauce and pasta are heated through, about 5 minutes. Remove from heat. Ladle into bowls and top with fennel fronds and toasted bread crumbs.
