In a 4-quart Dutch oven, heat butter over medium heat. Add onion; cook and stir about 5 minutes or until tender. Add beer, brown sugar, vinegar, caraway seeds, thyme, and Worcestershire sauce. Bring to boiling; reduce heat. Place bratwursts in beer mixture. Cover and simmer for 10 minutes.
Using tongs, remove bratwursts from cooking liquid. If desired, reserve cooking liquid. In a grill pan or a 10-inch skillet cook bratwursts over medium heat about 10 minutes or until brown and an instant-read thermometer inserted into bratwursts registers 160F, turning occasionally. If desired, return bratwursts to cooking liquid to keep warm until serving time.
To serve, place grilled bratwursts in buns. Using a slotted spoon, top with onion slices and Easy Cranberry-Pickle Relish. Makes 5 sandwiches.
Easy Cranberry-Pickle Relish
In a small bowl, combine canned whole cranberry sauce and sweet pickle relish.