2 pounds medium to large Yukon Gold potatoes (4 to 6 potatoes)
1/4 cup extra-virgin olive oil plus 1 tablespoon
Freshly ground black pepper
8 cornichons, finely chopped, plus 2 pickled onions from the jar, minced
2 tablespoons cider vinegar
3 tablespoons finely chopped dill
In a large saucepan, cover the potatoes with water and bring to a boil. Simmer over moderate heat until just tender when poked with a fork, about 10 minutes. Drain and let cool slightly.
Light a grill and preheat for at least 10 minutes or preheat a grill pan. Slice the potatoes crosswise 1/2 inch thick and transfer to a large bowl. Add 1 tablespoon of the olive oil, season with salt and pepper and toss.
Grill the potatoes over moderately high heat until dark brown grill marks form, about 5 minutes. Flip and grill until the potatoes are browned and completely tender, 4 to 5 minutes longer. Return the potatoes to the bowl.
In another large bowl, mix the cornichons with the pickled onions, the vinegar, dill and the remaining 1/4 cup of oil. Add the potatoes, season with salt and pepper and toss well. Let stand for at least 10 minutes, then serve warm or at room temperature.