Bring a pot of water and 2 tablespoons salt to a boil. Add potatoes and cook for 10-15 minutes or until fork tender. Drain and cut into quarters once cool enough to handle.
Preheat oven to 450 degrees F.
Line a baking pan with parchment paper. Place all potatoes on baking pan and drizzle with olive oil and season with 1 teaspoon salt and pepper.
Bake in oven for 25 minutes, or until golden brown.
While the potatoes are cooking, make the sauce and caramelized onions.
To make the caramelized onions, combine the onion and butter in a large skillet over medium heat. Stir gently to coat all onions in butter. Cut the heat down to medium-low and stir the onions only once every 5 minutes for 35 minutes. Deglaze the pan with the Mark West Black Pinot Noir, continue cooking for another 5 minutes, season with about ½ teaspoon salt, then cut off the heat and set the onions aside.
To make the sauce, combine mayonnaise, ketchup, relish, vinegar, and ½ teaspoon salt in a large bowl and whisk until smooth.
To make the dish, add all warm potatoes to a large, flat serving dish. Spoon sauce over top, then top with caramelized onions. Serve immediately.