The fish finger sandwich is the canonical case of a hot, crisp filling defended by everything around it. A fish finger is a baton of white fish, usually cod or pollock, set in a dry orange breadcrumb and fried or grilled until the crumb is brittle and the fish inside is just opaque. The whole sandwich is an argument for keeping that crumb intact between two slices of soft bread. Nothing else in the build is allowed to threaten it: the bread is yielding so it does not crush the coating, the sauce is cold so it cannot steam the crust soft, and the trip from pan to plate is kept short because the coating starts to surrender to its own residual heat the moment it is wrapped in bread. The filling brings every loud note the sandwich has, and the construction exists to deliver it before it can collapse.
The craft is contrast and restraint. The fingers carry the salt, the heat, and all of the texture, so each surrounding choice is made to stay quiet. Sliced white bread is preferred over a roll because it presses flat against the fingers and holds them in a row rather than letting them roll apart under the first bite. Butter to the edges is the seal: a thin fat film on the crumb that slows the bread from wicking up the inevitable trace of oil and going to paste underneath. The sauce, whatever it is, goes on in a measured stripe rather than a flood, because its job is to season and lubricate without drowning the coating it sits against. Three fingers laid side by side fill a slice more evenly than two thick ones, and a moment of pressing settles them so the sandwich holds together for the few bites it is built to last.
The variations are mostly arguments about the sauce and the cushion. Bound caper acid makes it the tartare version; sweet tomato makes it the ketchup version; a soft layer underneath makes it the mushy peas version; melted cheese forces a hot build rather than a cold one. The affectionate register turns the same sandwich into a butty, and the chip shop offers battered fish instead of crumbed for those who want it. Each deserves its own article rather than being crowded in here.