Buy lots of cannelé molds. As you can see here I’ve acquired a few different kinds over the years, and have made lousy cakes in all of them. The most expensive of these by far are the little copper cups in the middle there. Those are about two inches tall, hold a single cannelé each, and cost about twenty bucks (U.S.) apiece. I know what you’re thinking: maybe I can just buy a couple of the good ones and bake several rounds of batter in sequence. Not really, since each batch bakes for two hours. You’ll be up all night making four mouthfuls of cannelé at a go. Nope, unless you have lots of disposable income you’re going to want to go with silicone, at least to start. It doesn’t deliver an exterior nearly as crisp as the metal molds do, but at least you won’t be broke AND aggravated over a failed batch at the very same time.
I should add that traditionally the metal molds are lubricated with a 50-50 cocktail of melted butter and beeswax. That may be the super-secret key to a truly authentic cannelé, but then you can’t exactly get beeswax at the corner store. I find it’s best with these sorts of affairs to set your sights on what’s achievable first and pursue perfection later…after you get your next raise.