preheat oven to 425 degrees.

halve, peel, and finely dice onion.

cut potatoes into ½-inch wedges.

halve, peel, and finely mince shallot.

toss potatoes on a baking sheet with a drizzle of oil, ¾ tsp garlic powder (you’ll use the rest in the next step), salt, and pepper.

roast on top rack of oven until browned and crisp, 25-30 minutes.

meanwhile, in a small bowl, combine minced shallot, vinegar, 1 tsp sugar, and a pinch of salt.

in another small bowl, combine ketchup, mustard, sour cream, 1 tsp sugar, and remaining ¼ tsp garlic powder.

heat a drizzle of oil in a large pan over medium-high heat.

add onion and cook, stirring occasionally, until browned and softened, 5-7 minutes.

season with salt and pepper.

turn off heat; transfer to a plate.

while onion cooks, form beef into 2 patties, each slightly wider than a bun.

season generously with salt and pepper.

heat a drizzle of oil in same pan used to cook onion over medium-high heat.

add patties and cook almost to desired doneness, 3-5 minutes per side.

top with cheddar and cover until melted and patties are cooked to your liking, 1-2 minutes.

while cheese melts, toast buns in oven or toaster oven until golden brown.

drain pickled shallot, discarding liquid.

stir shallot into bowl with sauce.

fill buns with patties, onions, lettuce and sauce.

serve any extra sauce on the side for dipping potatoes into.