Cut the beef across the grain into into 1-inch pieces. Sprinkle with some salt, pepper and the flour and toss to coat the pieces. Set aside.
Fry the bacon in a Dutch oven or heavy pot until done then remove it with a slotted spoon, leaving the bacon drippings in the pan.
Working in batches and being careful not to overcrowd the pieces, generously brown the beef on all sides.
Transfer the beef to a plate and repeat until all the beef is browned.
Add the onions and fry them, adding more oil if necessary, until lightly browned, about 10 minutes. Add the garlic and cook for another minute. Add the vegetables and cook for another 5 minutes.
Add the Guinness and bring it to a rapid boil, deglazing the bottom of the pot (scraping up the browned bits on the bottom). Boil for 2 minutes.
Return the beef and bacon to the pot along with the remaining ingredients and stir to combine. (**At this point you can transfer everything to a slow cooker if you prefer. Follow the remaining steps and then cook on LOW for 6-8 hours or on HIGH for 3-4 hours.)
Bring it to a boil. Reduce the heat to low, cover and simmer for 2 hours. Add salt and pepper to taste.
Serve with some crusty country bread or Irish soda bread. This soup is even better the next day.