Disco,
If you feel like experimenting the next time you have brats, try this:
After poaching the sausages, strain the onions and reserve the beer. Put the onions in a heavy skillet over low heat with a pat of butter and caramelize them completely, until they're mahogany brown and sweet but not burned. Will probably take 30-40 minutes over low heat. Then add the beer back in, raise the heat and reduce by 2/3 or until sauce is fairly thick. Finish with a tablespoon or two of butter and season to taste. Be careful with salt, don't add any until the end. The reduced liquid will have salt from the brats being poached and the butter may have salt too, all of which will be concentrated when it's cooked down. I like to grate in a little nutmeg and add a little ginger and allspice for a nice earthy flavor. Serve it on your bratwurst on a roll.
I learned this recipe from a chef who was married to a girl from Wisconsin. Every time they'd go visit her folks he'd bring back a few pounds of brats and make them for us at the restaurant. He always used Guinness but it would work well with Negro Modelo as well. I've even made it with Miller Lite in a pinch. Wasn't the same, but wasn't bad.