In a heavy-bottom lidded ovenproof casserole dish or Dutch oven, heat the olive oil over medium-high heat. Add the meat in batches and sear each side until lightly browned on all sides. Place each batch onto a bowl until all the meat is browned. If the pan gets dry add a little more oil as needed.
Add the onions, garlic, celery, and carrots. Cook for 5 minutes, until the vegetables are starting to soften. More oil can be added if needed. Season with some salt and pepper.
Using a small sifter, sprinkle with the flour and cook, stirring often, for 2 to 3 minutes.
Add the 1 15.9 ounce can of Guinness Draught beer, stock, brown sugar, tomato paste, and dijon mustard. Bring to a boil, stirring and scraping to dissolve all the browned bits on the bottom of the pan.
Return the meat to the pan, along with the thyme and bay leaves. Season with salt and black pepper to your preferred taste and cover with the lid. Bring to a gentle boil then turn the heat to low and simmer gently for 2 hours.
Check the stew occasionally, stirring the pot.
Add the potatoes and continue to simmer for 1 hour, until the potatoes and meat are tender.At this point, I find adding a bit more beer adds more flavor to the final product. It can be up to half a can but keep a close eye on the consistency. This is optional. Season with salt and black pepper, remove and discard the bay leaves and thyme stems, and serve.
The stew can also be done in an oven at 325 degrees for 2 hours before adding the potatoes.