INGREDIENTS
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1/2 cup finely minced red onion
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3 tablespoons Dijon mustard
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3 tablespoons red wine vinegar, divided
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1/2 teaspoon sea salt
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Freshly ground black pepper
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1/2 cup extra-virgin olive oil
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1 teaspoon finely minced fresh tarragon leaves
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2 pounds Yukon gold potatoes, skin on, cut into 1-inch chunks
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2 cups diced tomato, skin on, including seeds and juice