Three milks and a thirsty sponge
The base is a light sponge, usually leavened mostly by whipped eggs, which gives it an open structure that can absorb liquid without falling apart. Once it cools, the baker pokes it all over and pours on a mixture of evaporated milk, sweetened condensed milk and either whole milk or heavy cream. The cake rests in the refrigerator, often overnight, until the liquid has worked its way through every layer. A topping of whipped cream or meringue goes on last.
A well-made tres leches is saturated but still holds its shape when sliced, with a little milk at the bottom of the container rather than a flood. A dry center means the soak was rushed; a cake that collapses into pudding means the sponge was too dense or too weak to carry the liquid.
A cake with several homelands
Its exact origin is debated. Nicaragua and Mexico both treat it as a national dessert, and versions are just as familiar in Guatemala, Honduras, El Salvador, Cuba, Puerto Rico and Colombia. Milk-soaked cakes have older European cousins, but the modern form leans on canned evaporated and condensed milk, which spread through Latin America in the 20th century, and recipes printed on milk cans are widely credited with making it popular.
Regional styles show up in US bakeries depending on who is baking. Nicaraguan-style cakes often wear a cooked meringue topping dusted with cinnamon. Mexican pastelerías tend toward stabilized whipped cream with strawberries, peaches or kiwi. Some bakeries make cuatro leches by adding dulce de leche or cajeta, a chocolate version soaked in chocolate milk, or a holiday cake spiked with rompope, the Mexican eggnog.
Ordering by the slice, the pan or the tier
Most bakeries that make it keep slices in plastic clamshells in the refrigerated case, typically $4 to $7 each. Whole cakes come as quarter or half sheets for parties, roughly $35 to $90 depending on size, and as round or tiered cakes decorated for quinceañeras, baptisms and weddings. Decorated tres leches needs a frosting that tolerates moisture, so expect whipped cream or a stabilized cream rather than fondant.
Because the cake needs time to soak, it usually can't be made from scratch the same day. Order whole cakes two to three days ahead, longer around Mother's Day (May 10 in Mexico), Christmas and graduation season.
Keep it cold
Dairy-heavy and egg-based, tres leches should go straight into the refrigerator and stay there except while it's being served. It keeps three to four days covered; past that, the sponge turns soggy. Do not leave it out on a buffet for hours in summer.
