Cook bacon in a Dutch oven or a large oven-safe pot with a lid over medium heat, turning occasionally, until evenly browned, about 10 minutes. Add butter, onions, and pinch of salt, and cook until onions are soft and translucent. Add garlic, and green onions, and cook stirring for 2 minutes.
Pour in beer, raise heat to high, and cook, stirring occasionally, until beer has reduced by about 75%. While beer is reducing, season with thyme, parsley, black pepper, salt, and pinch cayenne. Once beer has reduced, add potatoes and broth and bring to a simmer.
Preheat the oven to 300 degrees F (150 degrees C).
Prick sausage on both sides, and add to the pot on top of the other ingredients.
Cover and place pot into the preheated oven. Cook for about 2 1/2 hours. Remove the lid, and continue cooking uncovered for about 1 more hour.
Remove from oven and skim excess fat from top before serving. Garnish top with green onions, if desired.
