The Gerber gives up the second slice of bread and never pretends otherwise. It is half a length of garlic bread, buttered and run under the broiler with ham and Provel laid on top, eaten with a fork off the open face. The thing that defines it is Provel: a St. Louis processed cheese blend of cheddar, Swiss, and provolone formulated to go liquid and gummy rather than to pull, so it pools across the ham and the garlic crust into a single lacquered surface instead of a layer that slides off. That cheese is the entire reason the sandwich reads as itself and not as a slice of toast with ham on it.
The craft is broiler timing on a base built to take it. The bread is split, faced with butter and garlic, and toasted firm enough that it can carry molten cheese and the moisture the ham gives off without surrendering to mush before the fork gets there. The ham goes down first, thin and flat, so the Provel can seal it to the crust as it melts rather than letting it shift; the cheese is the binder and the flavor headline at once. Provel does not brown the way a pull cheese does, so the heat is judged by the bread and the bubble of the cheese, not by a blistered top. This is deli-counter and corner-bar food, assembled fast and slid under the salamander to order, eaten hot and open because closing it would only trap the steam and soften the one crisp thing in the build.
The variations stay close to the broiler and the open face. Some builds run the ham heavier or swap in a different deli meat; some add tomato under the cheese, which raises the moisture the crust has to fight; others lean the garlic harder. The wider St. Louis open-face shelf, the slinger and the diner hot plates that share the single-slice, knife-and-fork logic, runs the same idea with different toppings. Those deserve their own articles rather than being crowded in here.