¾ cup shredded Dubliner cheese (sharp aged that melts well)
Chop the potatoes into large chunks and place in a pot. Fill the pot with water until it covers the potatoes. Add a large pinch of salt. Cover the pot and bring to a boil. Once boiling, remove the lid, lower the heat, and simmer another 10 minutes—until fork tender.
While the potatoes are boiling, add 1 tablespoon of butter to a large skillet/pan over medium-high heat. Place the sausages into the skillet, allowing them to make contact with the skillet first, then add the sliced onions. Brown the “bangers” and onions for about 10 minutes.
Add the beer and allow it to reduce for another 10-12 minutes stirring occasionally.
Mix 1 tablespoon of soft butter with 1 tablespoon of flour together. Remove the bangers and mix the butter mixture into the beer reduction. It should thicken instantly. Now add the Worcestershire and stock to thin out the gravy to your desired consistency. Salt and pepper to taste.
Drain the potatoes and add butter and milk. Smash the potatoes with a potato masher. Once you’ve reached the desired consistency, stir in the cheese and mustard. Salt and pepper to taste.
Serve the bangers over the mash, topped with gravy.