On medium high heat, sauté the bacon so that the fat begins to render. Once bacon is cooked, remove and set aside.
Cut the chuck roast into bite-sized chunks. Dry the beef well with a paper towel and season with salt and pepper.
On medium-high heat, working in batches, sear the beef chunks in the bacon fat on all sides. Remove the beef and set aside. Turn heat down to medium.
Add the tomato paste, and stir constantly until a deep red/brown color develops.
Add the beer and scrape up the bits up from the bottom of the pot.
Now, add in the beef stock, Worcestershire sauce, thyme, bay leaves, brown sugar and bring to a simmer.
Add the beef, bacon, carrots, onion, garlic, and mushrooms to the pot. Lower the heat and simmer covered for about 1 hour and 15 minutes.
Uncover and add the potatoes for the last 45 minutes or so. Cooking the last bit uncovered will help the liquid reduce.
10-15 minutes before serving, stir in the cornstarch slurry and let the stew thicken a bit. This part is optional, only do it if you like more of a gravy consistency.
Remove the bay leaves and do a final check for salt and pepper.
Ladle the beef stew into bowls, grab a piece of lovely crusty bread, and start dunking.