Prepare bratwurst on a gas or charcoal grill according to package instructions.
Transfer fully cooked bratwurst to a large foil baking pan.
Place pan on grill; add cider (or desired liquid), butter, and sliced onions.
Allow brats to simmer over medium heat, covered, 15-20 minutes or until ready to serve.
Serve brats with onions on Martin’s Long Potato Rolls. Enjoy!