Salt and pepper the stew meat. Heat olive oil in a large, heavy pot over medium-high heat. Add butter, and as soon as it melts, brown half the stew meat until the outside gets nice and brown, about 2 minutes. Remove the meat from the pot, and add the rest of the meat to the pot and brown it, too. Remove it to the same plate. Set the meat aside.
Add the onion and garlic to the pot. Stir and coat it with the brown bits on the bottom of the pot. Cook for two minutes.
Add the tomato paste to the pot. Stir it into the onions and let it cook for two more minutes.
Pour in the beef stock, stirring constantly. Add the Worcestershire and sugar. Add the beef back to the pot, cover the pot, and reduce the heat to low. Simmer, covered, for 1 1/2 hours to 2 hours.
After 1 1/2 to 2 hours, add the diced potatoes and carrots to the pot. Stir to combine, put the lid back on the pot, and let it simmer for another 30 minutes. Add beef broth as needed to reach desired consistency.
Add parsley just prior to serving. Salt and pepper as needed.