Remove two-thirds of the fat from duck breasts, chop into chunks, and pass through a mincer.
Season meat and form into two balls, then stuff each with a scoop of Vacherin cheese and pat into burger shapes.
Preheat deep fat fryer oil to 160°C.
Rinse potato chips under cold water, dry thoroughly, and fry for 8-10 minutes until soft.
Drain chips on kitchen paper and increase oil temperature to 180°C.
Heat a griddle pan and fry burgers for 3-4 minutes per side until cooked through.
Caramelize sliced shallots on the griddle for 2 minutes.
Sauté mushrooms in butter for 3-4 minutes until softened.
Refry chips at 180°C for 2-3 minutes until golden-brown and crisp, then drain.
Serve the duck burgers with shallots and mushrooms inside brioche buns alongside the chips.