Add the beer, sliced onions, salt and pepper to a large pot. Bring to a boil over high heat.
Then add the bratwurst to the pot. Reduce the heat down to low and cook for 10-12 minutes until the bratwurst are cooked through.
Remove the bratwurst from the pan and continue to cook the onions on low heat for another 10-12 minutes while grilling the bratwurst.
Brush the grill grates with the olive oil to keep the bratwurst from sticking to the grates.
Place the bratwurst on the grill grates over direct heat. Cook for 5-8 minutes, rotating every 2 minutes, until the bratwurst are browned on all sides.
Remove from the grill. Serve on the buns topped with the onions, sauerkraut, ketchup and mustard. Enjoy!
Notes
Refrigerate any leftovers in an airtight container for up to 5-6 days. You can also pan fry the bratwurst in a large cast iron skillet instead of grilling them to brown them as well.