Brown: Pat sirloin dry. Heat avocado oil or olive oil in a heavy pot over medium-high. Brown beef chunks on all sides; remove.
Aromatics: Add sweet onions (and a splash of broth if needed to deglaze). Cook briefly; add garlic slices until fragrant.
Stew: Return beef. Add baby carrots, potatoes, beef broth, dried thyme, and sherry. Bring to a simmer.
Simmer: Cover and cook gently until beef and vegetables are tender, about 45-60 minutes for sirloin (do not invent thickener or tomato — card has neither; broth stays brothy unless reduced uncovered at the end).
Finish: Taste and adjust salt/pepper. Serve hot.