What Fat?
Most chefs feel that that no fat is required to cook burgers as the patties will cook in the meat’s rendered fat. If you decide you need a bit or if your burger is sticking to the pan and won’t flip, use a bit of neutral oil (sunflower, corn, rapeseed, etc.) to grease the pan. You can add a small dollop of butter or beef fat (dripping) to the pan towards the end of cooking for a bit of unctuous flavor and juiciness.