Cream, condensed milk and milk set with gelatine over a layer of biscuits and left in the fridge. Nothing is baked and nothing is a cake: it is the no-bake version of tres leches, and the waiting is most of it.
This is not a tres leches cake and it is worth saying plainly, because the two share a name and almost nothing else. A tres leches cake is a sponge, baked, then soaked in evaporated milk, condensed milk and cream until it is saturated. This is a refrigerator dessert: no oven, no sponge, a layer of biscuits at the bottom and a set cream on top. Both are good and they are different dishes. Let the gelatine cool before it goes into the blender with the cold milks. Poured in hot it sets into fine threads on contact and they never disappear. The setting takes longer than most people expect. The recipe says it can take up to a day and it is not exaggerating: a deep dish of gelatine-set cream needs many hours, and it is ready when the surface springs back under a finger. Make it the day before. Moistening the biscuits is optional and it changes the dessert. Dry, they stay crisp underneath; moistened, they soften into something closer to a cake layer.