Place sliced red onion in a bowl with red wine vinegar and sugar to pickle.
Season beef mince and shape into four 150g patties.
Whisk egg yolks while gradually adding oil until the mayonnaise becomes creamy.
Stir in mustard and vinegar, season, and refrigerate the mayonnaise.
Heat vegetable oil in a deep fat fryer to 130°C.
Fry rosemary for 30 seconds, drain, chop finely, and mix with sea salt.
Steam the chunky potato chips for 15 minutes.
Deep fry the chips at 130°C for 3 to 4 minutes and drain.
Increase oil heat to 180°C, fry chips until crisp, and toss with rosemary salt.
Cook burgers under a hot grill for 4 to 5 minutes per side.
Assemble burgers on rolls with toppings and serve with chips and mayonnaise.