Heat olive oil in large dutch oven on high heat.
Dust cubed chuck roast with flour, and generous amounts of salt and pepper.
Brown beef cubes on all sides in batches being careful to not overcrowd for about 5 minutes per batch.
Remove beef to a large bowl after browning.
Melt 1 tablespoon butter on medium high heat.
Add mushrooms and a dash of salt.
Lightly brown mushrooms and remove to beef bowl.
Add additional tablespoon of butter if needed and saute carrots, celery, and onion until slightly browned about 3-5 minutes.
Incorporate tomato paste, thyme, parlsey, and garlic and cook and additional 1-2 minutes.
Add Guinness and bring to a boil scrapping any browned bits from the bottom of the pot.
Allow Guinness to reduce for 1-2 minutes.
Pour in beef stock and return to a gentle simmer.
Cover and simmer for 2.5 hours or until beef has reached desired tenderness.
Remove lid and bring stew to a rolling boil.
Taste check to see if additional salt and pepper is needed.
Skim fat if necessary.
If stew consistency is not as thick as desired, add a strained slurry of 2 tablespoons flour mixed with 1/2 cup stock.
Continue to vigorously simmer for an additional 5-10 minutes allowing stew to thicken.
Serve over mashed red potatoes made with half and half, salt, pepper, and parsley.
Garnish with additional parsley if desired.