Preheat oven to 300° F.
Place a large Dutch Oven on the stove. Over medium heat, render the bacon. You want it cooked, but not crispy. Use a slotted spoon to remove the cooked bacon to a plate and set aside.
Carefully add the sausages to the Dutch oven. Brown on all sides, about 2 to 3 minutes per side. Remove and reserve to same plate as bacon.
Discard all but 1 or 2 tablespoons of the rendered fat. Add the onions. Sauté until the onions just begin to break down, 5 to 8 minutes. Toss onions several times to ensure they are breaking down evenly. Sprinkle the sugar over the onions and toss again. Add the garlic. Sauté until fragrant, 1-2 minutes.
Off the pot from the heat briefly and deglaze with crème sherry. Replace pot atop heat and bring the sherry mixture to a boil. Use the back of a spoon to scrape up all of the fond at the bottom of the pan. Reduce the heat to medium low and reduce the sherry until all of it has largely evaporated and the onions are caramelized. Pour in the stout ** see NOTES. Again bring to a boil before lowering the heat and allowing the stout to largely evaporate. Remove the pot from the heat again. Remove the onions from the pot to a bowl. Set aside.
Add half the chunked potatoes to the bottom of the Dutch oven. Season liberally with pepper and add half the chopped parsley. Add half the onions. Finish with half the cooked bacon. Repeat beginning with the remaining potatoes and ending with the remaining cooked bacon.
Nestle the bangers atop the layers. Add the chicken broth all at once. Replace the pot (very heavy now) to the heat and bring to another boil. Off the pot from the heat and fit the pot with its lid. Carefully transfer the pot to the oven.
Braise for 2 to 4 hours checking every 30 minutes to see if broth must be added. Maintain an inch of liquid at all times to prevent burning. ** The braise is largely complete at 2 hours. Adding additional time ensures a well flavored pot liquor and very tender potatoes. I braise for a minimum of 3 hours and use the last hour to set my table and prepare my biscuits.
Season with salt and pepper if necessary. If planning to mash some or all of the potato mixture, carefully spoon out to a bowl and use a hand masher to 'rough mash' the potatoes. I use about 1/2 cup of the pot liquor to mash in lieu of butter or milk.
Serve by mounding some of the mash in a bowl. Ladle some remaining stew and the pot liquor over top and nestle a banger right in the middle.