Dulce de leche is a thick, caramelized milk confection, served as a dessert on its own and used as a topping or filling for tarts, cakes, and pastries. It's made slowly, cooking milk and sugar down until they turn a deep golden caramel — mostly a matter of patience until the final stretch.
The dulce de leche is ready when it turns caramel colored and you can see the bottom of the pan as a spoon is drawn across it, or when a spoonful holds its shape on a plate.