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 a 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 it has reduced by about 75%. While the beer is reducing, season with thyme, parsley, black pepper, salt, and a pinch of cayenne. Once the 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 the 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 garnish top with green onions, if desired. Serve!