The batters may appear to mix when you pour them into the pan, but they completely separate while baking, with the flan ending up on the bottom when it's inverted. I like eating it warm, but traditionally, it is chilled 24 hours before serving. Flan is a rich, creamy, cooked egg custard. It is often flavored with vanilla and baked in a water bath to retain its delicacy. Cajeta is a thick and creamy spread or paste made with caramelized sugar and milk. It is used as a desert on its own or as a topping. Also known as "dolce de leche," it is sold in many supermarkets, Latin specialty markets or online. It can be substituted with a thick caramel sauce.