Backyard Red Potato Salad

Place potatoes in a large saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook for 10 minutes. Drain; cool slightly. Cut each in half. In a large bowl, combine the potatoes, onion, 1/4 cup oil, 1/2 teaspoon salt and 1/4 teaspoon pepper; toss to coat. Arrange cut sides down on a grilling grid; place on a grill rack. Grill, covered, over medium heat for 8-10 minutes or until vegetables are tender and lightly browned, turning occasionally. Chop onion. Place onion and potatoes in bowl. In a small bowl, whisk the vinegar, lemon juice, mustard, sugar, garlic and remaining oil, salt and pepper. Add to potato mixture; toss to coat. Sprinkle with tarragon. Serve warm or at room temperature. Refrigerate leftovers.