Hosting a barbecue for a large group -- your child's junior football team, for example, or a family reunion -- can be a great way to bring people together, but it requires some planning if you want the food to be ready for everyone at about the same time. Most barbecue grills can only handle so many burgers at once. Rather than spending hours during your party grilling individual batches, you might decide to cook them all in advance, and then simply reheat them when it's time to eat.
Set your oven to 175 degrees C (350F).
Remove fully cooked burgers from the fridge or freezer and place them in single layers on baking trays.
Place the sheets of burgers in the oven. Monitor the burgers periodically as they reheat, as individual ovens heat at different rates. Refrigerated burgers may need to cook for 10 to 15 minutes, while frozen burgers can take 20 minutes or more to warm up.
Insert the tip of a cooking thermometer into the burgers when the time is almost up. They need to reach an internal temperature of 74 degrees C (165F). If they aren't quite there yet, reset your timer.
Put warmed burgers on a platter, and cover it with foil to seal in the heat. Bring it to your table and invite your guests to dig in.