The St. Paul sandwich takes a dish that is normally eaten with a fork under gravy and turns it into a cold-handled filling. The center is an egg foo young patty: beaten egg bound with bean sprouts, onion, and usually a little meat, fried in a hot pan into a dense, set disc with crisp lacy edges. On a St. Louis Chinese-American counter that patty is pulled off the heat, drained, and slid between two slices of plain white bread with mayonnaise, dill pickle, raw onion, and a leaf of iceberg. No sauce, no gravy, no plate. That is the whole counterintuitive move: the foo young patty is treated as a self-contained protein slab the way a cooked burger or a fried fillet would be, and the sandwich is built around keeping it that way.
The patty is doing all the structural work, so the way it is cooked decides whether the sandwich holds. It has to be fried firm enough to lift and bite without the egg tearing apart in the hand, and drained well enough that it does not weep into the bread before it reaches the counter. The mayonnaise is functional as much as it is flavor: spread to both slices, it waterproofs the soft crumb against a still-warm patty so the bread survives the trip out the door. The pickle and raw onion are the sharp, acidic counter to a rich egg-and-grease center, and the iceberg adds the cold crunch the patty has none of. White bread is chosen precisely because it has no chew and no agenda; a crusty roll would fight a tender egg disc and win.
This is a tightly local sandwich, and its variations are the foo young menu folded into the same frame: a shrimp patty, a pork or chicken patty, a plain egg version, a heavier hand on the sprouts. The wider field of Chinese-American counter cooking and the dense long tail of place-named regional specialties run alongside it, and those deserve their own articles rather than being crowded in here.