Trick-or-treating looks like an American invention. The trick half more or less is. The treat half is English, Welsh and several hundred years older than anyone in a Spider-Man costume.
The custom
Souling was the practice of going door to door around All Souls' Day — 2 November — to ask for soul cakes. In return, the souler prayed for the dead of that household. The medieval logic was concrete: prayer shortened a soul's time in purgatory, and the poor had prayer to give when they had nothing else.
The tradition is traceable to at least the sixteenth century and was strongest in northern and western England — Shropshire, Cheshire, Lancashire, the Welsh borders — and in Wales itself. Soulers often went in groups, singing a souling song, and in some districts the custom merged with mumming: performance troupes in disguise, working the doors with a play or a dance.
That combination — a disguise, a performance, a door, a reward — is trick-or-treating entire. It simply crossed the Atlantic, lost the prayers, and gained the threat.
What a soul cake actually is
Closer to a biscuit than a cake: small, round, enriched with butter and spice. Nutmeg, cinnamon, ginger and allspice, often with currants, and traditionally marked with a cross on top — one cake, one soul.
They are genuinely good, and quite unlike modern Halloween food in that they taste of something other than sugar. English Heritage has served them at Halloween openings, and any decent shortbread method will get you there.
The song
Souling songs survive in several versions across the west of England. The best known runs:
A soul, a soul, a soul cake, Please good missus, a soul cake. An apple, a pear, a plum or a cherry, Any good thing to make us all merry.
There is an obvious continuity with wassailing at midwinter and with the general English habit of turning up at a neighbour's door with a song and an expectation. It is the same social machinery: the community licensing the poor to ask, once a year, without shame attaching to it.
Where the trick came from
The threat is the newer part. Mumming always carried a faint edge — a masked group at your door on a dark night is not purely charming — and English Mischief Night supplied a separate, thriving tradition of licensed vandalism. In America the two fused into the modern formula, with "trick or treat" recorded from the 1920s and 30s.
So when someone tells you trick-or-treating is an American import, the accurate version is: the phrasing is American, the sweets are American, and the practice of knocking on doors in disguise for food on the night of the dead was being done in Shropshire long before Massachusetts existed.
Trying it
Bake a batch on 1 or 2 November rather than the 31st, which is when soulers actually went. Spiced, marked with a cross, handed out at the door. If someone asks what they are, you can tell them they are eating the ancestor of the Mars bar in their child's bucket.