How to Make It
In a large saucepan, cover the potatoes with water and bring to a boil. Add a generous pinch of salt and cook over moderately high heat until tender, about 20 minutes. Drain and spread on a baking sheet to cool, then cut in half.
Meanwhile, in a large bowl, mix the red onion with the Champagne vinegar and let stand for 10 minutes.
Light a grill and oil the grate. Grill the potatoes cut side down over moderately high heat until lightly charred, about 5 minutes. Transfer to the bowl with the onions. Add the 1/4 cup of olive oil and mix well. Let cool completely. Stir in the parsley and season with salt and pepper. Top with the chips; serve.