Rubbing the cut sides of the garlic and the fresh thyme leaves all over the beef sirloin. Dump the beef into a big dish, drizzle with olive oil and rub it deep into every crevice of the meat.
(Skimp on this step if you have to, but let cover and refrigerate for 1–2 days if you can afford the time—it concentrates the meaty richness and elevates every single bite.)
If you’d prefer to forgo the marinade, move directly to the next step.