The top three bars in Nanaimo. Dessert, that is.

What the thing actually is

A Nanaimo bar is three layers and no baking past the first one. The bottom is a pressed crumb base — graham, coconut, cocoa, usually walnuts, bound with butter and egg. The middle is a pale custard buttercream, and the custard powder is not optional if you want the flavour people expect. The top is a thin sheet of chocolate that has to be thin enough to yield to a fork and thick enough to snap.

That last part is where most of them fail. A chocolate lid that shatters and slides off the custard is a bar made by someone in a hurry. The good ones are scored or cut while the chocolate is still setting, which is a small thing you can taste.

The top three, as promised

Not premises — versions. Anyone who tells you there is one correct Nanaimo bar has not eaten enough of them.

• The classic

  Yellow custard, walnut in the base, chocolate on top. The benchmark. If a bakery gets this one right, trust them with the rest of the case.

• The flavoured middle

  Mint, peanut butter, coffee, occasionally something with a liqueur in it. The mint version is the one that starts arguments, and it has more defenders than you would expect.

• The engineered ones

  Cheesecakes, ice creams, milkshakes and martinis built on the same three flavours. Mostly a tourist sport, and mostly good anyway.

Doing it properly

Nanaimo runs a self-guided dessert trail through cafés and bakeries around the city, and the current list of stops lives with local tourism rather than with us — worth looking up before you go, because it changes. Spread it over a couple of afternoons. Three bars in one sitting is not research, it is a decision you will regret near the harbour.

Go on foot if you can. The waterfront walkway strings a good number of the downtown stops together, which turns the whole exercise into a walk with punctuation.

The part that isn't about dessert

There is a real reason a dessert crawl tells you something about a town. You end up walking its centre at an ordinary pace, on an ordinary day, stopping every twenty minutes. You notice the benches, the hills, whether the crossings give you enough time, and whether anyone says hello.

That is most of what a first visit should be doing anyway. The bars are just a better excuse than driving past houses.