Preheat the oven to 325 degrees.
Cook the bacon pieces in a large Dutch oven over medium heat until cooked through and the fat has rendered down.
Remove the bacon with a slotted spoon and place on a paper towel. Remove all but 1 1/2 tablespoons of bacon grease from the Dutch oven; set the remaining bacon grease aside until needed.
Return the Dutch oven to the stove and turn it up to medium-high. Pat the beef chunks dry then season well with sea salt and freshly cracked pepper, to taste.
Add half of the meat to the HOT dutch oven and cook, until browned all over, about 3 minutes. Remove the beef from the Dutch oven to a plate.
Add the remaining beef to the Dutch oven and cook the beef until browned all over, about 3 minutes. Remove to the plate; set aside.
Add the remaining 1 1/2 tablespoons of bacon grease to Dutch oven and reduce to medium heat.
Add the onion and cook, stirring often, until softened, about 3 minutes.
Add the minced garlic and cook, stirring constantly, for 30 seconds.
Add the flour and cook, stirring it into the onion mixture constantly, for 1 minute.
Add the Guinness and whisk until the mixture is well combined and the flour is dissolved, about 2 minutes.
Add the tomato paste and whisk until well combined then add the beef broth.
Add the plate of cooked beef chunks and their juices along with the carrot, celery, bacon crumbles, thyme sprigs, and bay leaves. Side Note: If the beef and vegetables aren't submerged in liquid, add more beef broth until they are.
Cover with a tight fitting lid and place into the oven to cook for 2 hours and 25 minutes.
Remove the lid after 2 hours & 25 minutes and continue to cook for 20 minutes to allow the beef to finish cooking and the sauce to thicken slightly.
Remove from the oven and skim off any fat from the surface. Remove the thyme sprigs and bay leaves. Taste and season with sea salt and freshly cracked pepper, to taste.
Serve over creamy mashed potatoes. Enjoy.