Preheat the oven to 350° and line a baking sheet with parchment paper or foil. Using a 2-inch round biscuit cutter, cut the Potato slices into rounds. In a bowl, toss the potatoes with the olive oil and arrange them in a single layer on the baking sheet. Season lightly with salt and pepper, then sprinkle with the Cheese. Bake the Potato rounds for about 45 minutes, or until deep golden; let cool. Transfer the Potato coins to paper towels. In a small bowl, combine the Ham with the Mayonnaise, scallion, Cornichons, capers, tarragon and mustard. Season with salt and pepper. Spoon the Ham salad onto the Potato coins and serve.