Step 1: Prepare the Pickle-Brined Onions (Optional, but Recommended). In a small bowl, combine the dill pickle brine with 1/2 of the chopped onions. Let it sit while preparing the other ingredients.

Step 2: Cook the Bacon. In a Dutch oven or large, oven-safe pot with a lid, cook the bacon over medium heat, turning occasionally, until evenly browned, about 10 minutes.

Step 3: Sauté Onions and Garlic. Add the butter and remaining (non-brined) onions and a pinch of salt to the pot with the bacon. Cook, stirring occasionally, until the onions are softened and translucent, 7 to 10 minutes. Add the garlic and green onions and cook, stirring, for 2 minutes more.

Step 4: Deglaze with Beer. Pour in the stout beer, raise the heat to high, and cook, stirring occasionally, until the beer has reduced by about 75%.

Step 5: Add Seasonings. While the beer is reducing, season the mixture with the thyme, parsley, black pepper, salt, and cayenne pepper (if using).

Step 6: Add Potatoes and Broth. Once the beer has reduced, add the potatoes and chicken broth to the pot. Bring to a simmer. Add the drained, pickle-brined onions.

Step 7: Preheat Oven. Preheat the oven to 300 degrees F (150 degrees C).

Step 8: Add Sausages. Prick the sausage links on both sides with a fork. Add the sausages to the pot on top of the other ingredients.

Step 9: Bake (Covered). Cover the pot and place it in the preheated oven. Cook for about 2 ½ hours.

Step 10: Bake (Uncovered). Remove the lid and continue cooking, uncovered, for about 1 more hour. This will allow the sausages to brown and the broth to thicken slightly.

Step 11: Skim Fat (Optional). Remove the pot from the oven and skim off any excess fat from the top of the stew before serving.

Step 12: Serve and Garnish. Ladle the Dublin Coddle into bowls. Garnish with additional chopped green onions and pickled mustard seeds (if using). Serve hot, with dill pickle spears on the side.