"Sautéed leeks and toasted brown mustard seeds punch up this picnic classic...."
INGREDIENTS
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3 1/2 pounds fingerling potatoes, unpeeled, cut into 3/4"?1" pieces
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1 tablespoon kosher salt plus more for seasoning
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9 tablespoons (or more) extra-virgin olive oil, divided
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2 tablespoons brown mustard seeds
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3 medium leeks (white and palegreen parts only), halved lengthwise, cut crosswise into ¼" slices (about 5 cups)
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1 tablespoon (or more) white wine vinegar
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1 tablespoon Dijon mustard
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Freshly ground black pepper