In a medium pot with a steamer basket, add 1 inch of water and the potatoes. Bring to a simmer, cover, and cook for 10-12 minutes, or until fork-tender. Drain the potatoes.
In a large bowl, combine the remaining potato salad ingredients. Fold in the potatoes and season with salt and pepper to taste.
Heat a skillet over medium and cook the bacon until crisp, turning once. Transfer to a paper towel-lined plate to drain.
Blend the burger sauce ingredients in a blender until smooth. Season to taste.
Shape the beef into 4 patties. Season liberally with salt and pepper.
Heat the oil in a skillet over medium heat. When hot, add the patties and cook, flipping once, until seared on each side and cooked all the way through, about 8 minutes. Add the cheese after flipping.
Serve the burgers on brioche buns with onion, lettuce, tomatoes, pickles, bacon and sauce.