In a bowl toss the beef with the flour and a pinch of salt and pepper until it is all coated.
In a large heavy-based pot drizzle in the olive oil then add in the flour-coated beef and onions. Saute on high for 5-8 minutes or until the beef is browned all over.
Deglaze the pot with the beef stock and red wine so that all the tasty nearly bits on the bottom of the pot come off.
Add in the carrots, potatoes, celery, garlic, bay leaves, rosemary, tomato paste and Worcestershire sauce. Give it a stir and cover and cook on low for 45 minutes, stirring occasionally.
Add the zucchini into the pot and stir, then cook it again for 15 minutes.
Use a spoon to check the thickness of the sauce. If the sauce isn’t thick enough but the meat and veggies are cooked through just mix the cornstarch with 3 tablespoons water and then stir it into the pot. Cook it for another 10 - 15 minutes, stirring constantly until the stew has thickened.