Heat 2 tablespoons of olive oil in a Dutch oven over medium-high heat for 2 minutes. Turn the heat down to medium-low and brown the beef in three batches, turning the pieces occasionally. Deglaze the pan with ¼-½ cup of water and scrape off the browned bits of meat, then pour the liquid into a bowl for later.
Melt the other tablespoon of oil in the Dutch oven over medium-high heat, then add the onions and cook until they're golden, stirring occasionally. Add the celery and carrot and cook for 5 more minutes, until the celery is beginning to soften.
Add the browned beef, beef stock, salt, pepper, and bunch of thyme, then cover and bring to a boil. Turn the heat down to low and simmer for 1½ hours, or until the meat is tender. Remove the bunch of thyme.
Stir in the turnip and potatoes, then simmer for another 35-40 minutes, until the potatoes are tender and have thickened the gravy a little.
Adjust seasonings to taste, then pour the filling into a 6-cup (1.5 liter) pie dish. Reserve any extra filling to eat separately.