INGREDIENTS
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2 pounds medium red bliss potatoes
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6 tablespoons sherry vinegar
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2 tablespoons Dijon mustard
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1 tablespoon drained capers, chopped, plus 1 teaspoon caper brine
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6 cornichons, cut into 1/4-inch pieces, plus 1 tablespoon cornichon brine
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1/4 cup extra-virgin olive oil
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1/2 cup canola oil (see Cook's Note)
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3 sprigs fresh rosemary
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3 teaspoons kosher salt