Rub the beef leg slices with the garlic clove on both sides. Season generously with salt and coarsely ground pepper.
Heat clarified butter in a large pot or braising pan over medium-high heat. Brown the beef leg slices on both sides until golden brown, about 8-10 minutes total. Remove and set aside. In the same pot, brown the whole peeled onions over medium heat until lightly golden, about 5-8 minutes.
Return the beef to the pot and add the bay leaf. Pour in the red wine and beef stock, scraping the bottom of the pot to deglaze. Reduce heat to low, cover with a lid, and braise for approximately 2 hours. Stir every 20 minutes and ensure there is always enough liquid to partially cover the beef.
Remove from heat. Taste the sauce and adjust seasoning with salt and pepper if needed. Stir in the cream. Serve the beef and onions in the sauce.