Heat the olive oil in a Dutch oven over medium-high heat. Add the beef cubes in a single layer and brown on all sides, about 6-8 minutes total. Remove the beef to a plate.
Lower the heat to medium. Add the leeks and carrots to the pot and cook until the leeks soften, about 5 minutes. Stir in the garlic and cook for 1 minute more.
Sprinkle the flour over the vegetables and stir for 1 minute to coat everything. Pour in the ale and beef broth, scraping the bottom of the pot to release any browned bits.
Return the beef to the pot along with the celery root, thyme sprigs, and bay leaves. Season with salt and black pepper. Bring the mixture to a simmer.
Cover the Dutch oven and transfer it to a 325°F oven. Cook for 2 hours, or until the beef is tender and the celery root is cooked through. Remove the thyme sprigs and bay leaves before serving.