Preheat oven to 300 degrees.
In a large dutch oven, cook the bacon on medium heat until crispy. Remove the bacon using a slotted spoon & drain on paper towels. Sear the sausage (or bratwurst) in the bacon grease to brown. Remove the sausages from the pan to drain with the bacon.
Remove all but about 1/4 of bacon grease from the pan. Add the sliced onion to the pot, & cover. Cook for about 7 minutes, stirring once or twice. Add in the chicken broth, apple cider vinegar, minced garlic, & a sprinkling of pepper. Bring to a boil, then remove from the heat. Pour the onion/broth mixture into a separate dish for a moment.
Layer the sliced potatoes along the bottom of your dutch oven. Pour the onion/broth mixture over top. Add in 1/2 of the cooked bacon & 1/4 cup of chopped fresh parsley. Place the whole sausages on top.
Cover, cook for 45 minutes. Remove from the heat & pour in 1 cup of Guinness beer (or broth). Replace the cover & return to the oven for another 45 minutes.
Top with the remaining bacon & a few more sprinkles of fresh parsley once it's done. Serve with crusty bread to sop up the au jus.
*If you want all your bacon crispy, then save it all for the end.