Obleas con Cajeta

The oblea is a thin baked wafer of European, ultimately convent and church origin — the same kind of thin flour-and-water wafer once made for communion — that came to Mexico with Spanish baking and became a popular sweet, colored and sold in markets. Cajeta is the goat's-milk caramel of central Mexico, most famously of Celaya in Guanajuato, made by slowly cooking down goat's milk with sugar. Pairing the two — a smear of cajeta between colored wafers — is a long-standing street and market combination rather than a dated invention with a single creator; the oblea de cajeta is simply one of the everyday ways cajeta is sold and eaten. As a folk sweet it carries no fixed origin date. The wafers are sometimes also eaten with other fillings, but cajeta is the classic.

The first thing is the wafer's crisp snap, a clean dry crackle that gives almost no resistance, like biting a thin sheet of edible paper. Then the cajeta takes over: a thick, sticky, deeply caramelized goat's-milk caramel, sweet and rich with the particular tangy, faintly bitter depth that burnt goat's milk gives that cow's-milk caramel does not. The wafer melts to nothing on the tongue while the caramel clings and pulls. Where nuts or coconut are folded in, they add crunch against the smooth caramel. It is light to hold but very sweet to eat, the brittle wafer and the chewy caramel playing off each other.

Two very different techniques meet in one sweet. The oblea is a thin baked wafer: a runny batter of flour (or starch) and water, sometimes a little oil and color, is spread between two hot flat irons or plates and baked crisp in seconds, the way a communion wafer or a pizzelle is made — almost all the water flashes off, leaving a dry, brittle, glassy-thin disc. The cajeta is the opposite kind of cooking: goat's milk is simmered down for a long time with sugar and a little baking soda until it thickens to a pourable caramel, the soda nudging up the pH so the milk browns readily through the Maillard reaction, building the deep color and the toffee-tangy flavor; goat's milk caramelizes sharper and tangier than cow's because of its higher share of short-chain fatty acids. The finished sweet is just assembly: a generous layer of thick cajeta spread on one wafer and capped with another, the caramel acting as both filling and glue. It is best eaten soon after building, while the wafer is still crisp, before the moisture in the caramel begins to soften it.