Season beef very generously with salt and pepper. Add oil to a large heavy pot or Dutch oven with tight fitting lid, and set over high heat. When oil begins to smoke slightly, add beef and brown very well. Work in batches if needed. Once it is well browned, transfer beef to bowl using slotted spoon, leaving the oil and beef drippings in the pan.
Reduce heat to medium, add onions to pan and saute for about 5 minutes or til translucent. Add flour and cook for 2 minutes, stirring frequently. Add garlic and cook 1 minute. Whisk in 1 cup of the stock to deglaze bottom of pan, scraping up any browned bits that are stuck to the bottom.
Add remaining broth, carrots, celery, ketchup, bay leaf, rosemary, thyme, beef and salt. Bring back to gentle simmer, cover and cook over low heat for 1 hour. Add potatoes and simmer, covered for another 30 minutes. Remove cover, increase heat to medium and cook, stirring occasionally, for another 30 minutes, or til meat and vegetables are tender. This final 30 minutes of cooking will reduce and thicken the sauce. If the stew gets too thick, add more stock or water.
Turn off heat, taste and adjust seasoning, then let sit for 15 minutes before serving. Garnish with parsley if using.