Whisk together the mayo, mustard, and horseradish in a small bowl.
Cover and refrigerate for at least 30 minutes.
Divide the meat into 4 equal portions.
Roll each portion into a 3/4" thick burger and take your thumb and press it down in the middle of the burger to make a divot. This is how you keep your burgers from becoming big meat balls on the grill.
Season both sides of the burger with salt and pepper.
Grill for 3-4 minutes flip
Wait 2 minutes and top each one with 2 slices of cheese per burger
Spread the horseradish sauce on the top and bottom buns, be liberal.
Place the burgers on the bun bottoms and top with tomato, lettuce, and onion.
Pile on the potato chips and put on the top bun.