The steak de Burgo sandwich is built around a sauce that is doing the work of a marinade, a baste, and a dressing at once. Steak de Burgo as a plate is a Des Moines Italian-American tenderloin finished in butter heavy with garlic and herb, and the sandwich version keeps that garlic butter as its defining element rather than treating it as a pan drippings afterthought. The butter is what makes this more than a steak between bread: it carries the garlic and herb into the crumb, glosses every slice, and supplies the richness and seasoning the bread would otherwise lack. Strip the garlic butter out and it collapses into a plain steak sandwich; the sauce is the recipe.
The craft is in the cut and the timing of the butter. Tenderloin is lean and has almost no internal fat to protect it, so it is seared fast to set a crust and then basted in the foaming garlic butter rather than cooked through in it, kept short of well done so it stays tender enough to bite cleanly through bread. The meat is sliced rather than served whole so the load distributes along the roll and the butter can reach every bite. The bread has to be sturdy enough to absorb a butter-and-jus soak without going to mush at the midpoint, which is why a roll with real structure rather than a soft bun is the sensible choice; a slick filling on a weak roll fails fast. The garlic butter is applied warm at assembly so it soaks in rather than setting on the surface.
This is a strongly local Des Moines sandwich, and the variations follow the plate it descends from: a cream-finished version, a heavier garlic hand, the herb skewed toward basil or toward a peppery profile, the steak left whole on a knife-and-fork plate rather than folded into bread. The wider Italian-American steak tradition and the dense field of place-named regional specialties run nearby, and those deserve their own articles rather than being crowded in here.