I ate at least one brat a day from Friday to Monday over Memorial Day weekend. I bought a grilled brat on Friday, grilled my own on Saturday and Sunday, and made these for a small party at our place on Sunday
Since I was making other things, and wanted the brats to be ready when guests were ready to eat them, I grilled them slightly, and gave them the hot tub treatment in a disposable roasting pan filled with beer and caramelized onions, where they barely simmered until ready to eat. This is the classic (Midwestern) way to prepare sausages for a crowd. I do sauté onions for at least 4o minutes on the stovetop before putting them in the beer bath.