Melt the butter in a large skillet and sauté the onion until softened.
Add the bratwurst and lightly brown on both sides. Pour in about 12 oz of Paulaner Oktoberfest Bier, then stir in the mustard, brown sugar and caraway seeds.
Cover and gently simmer for 15–20 minutes, turning the bratwurst occasionally. Remove the lid and cook a few more minutes to reduce the beer and onion mixture.
Serve with sauerkraut, German mustard and a warm pretzel—and, of course, a cold Paulaner Oktoberfest Bier.