Heat a dutch oven over medium high heat. Add in the brats, beer, and onions. Simmer the sausages and onions, turning the sausages occasionally and gently stirring the onions, about 10 minutes or until the beer's reduced to syrup and the onions are caramelized.
Push the sausages to the edges of the pot. Stir in the beef broth, de-galzing the pan, and scraping up all the crispy bits. Push the meat back to teh center of the pot, and continue simmering for 10 minutes, or until the sausages are cooked through.
Bring the mixture to a boil, and boil-stirring occasionally- just until the sauce has reduced and once again turned syrupy.
Reduce the heat to medium low. Add the butter. Stir it getting up any crispy bits stuck to the bottom.
Push the brats back into the middle of the pot. Add the sauerkraut in around the brats. Continue cooking, turning the sausages and stirring the sauerkraut often, until the sauerkraut's heated through and a little bit crisp.
Stir the peas into the sauerkraut, again heating just until they're heated through. Remember to stir/turn so nothing burns!
Salt & pepper the sauerkraut to taste, serve, and enjoy!