Dulche de leche is a milk based caramel sauce that I see increasingly on the sweet side of the kitchen. As the name suggests it is very popular in Latin cuisine but in shows up in other nationalities as well under the disguise of other names. It is usually made by simmering milk and sugar, reducing about 4 or 5 times the amount of liquid you started with. The sugar and the sugars in the milk will caramelize (maillard reaction) and will turn a darker more caramel-y color.
Traditionally used for pastry work its great on muffins, cake, flan, etc. I think it is an amazing topping for strawberries, ice cream, breakfast breads, pancakes, and even toast. I made some yesterday to go with an apple pie, and would be good to have to dip apples, pears, and even some dried fruits.
Rather than go through the whole process of reducing milk, I like to take a can of sweetened condensed milk from the store and remove the label and shake it well. Cover it totally with water in a saucepan big enough to leave yourself at least a few inches of water covering. Then give it medium ish heat for about 2-3 hours. Remove from pan and place can in the fridge for at least a few hours as it may come oozing out the top when you try to open the can while hot. If you find the consistency isn't exactly what you want when you go to use it, it will thin with just a touch of heat in a microwave, and be a bit more pliable.
You are simmering a can here so monitor your heat as boiling could cause rupture, and make sure to keep it covered with water, adding, if needed, as water evaporates to ensure you are going to have even cooking. I cant keep it around long enough to tell you how long the shelf life will be, but i would imagine it would be good for at least 2 weeks as the sugar content is so high bacteria isn't going to be very interested in it. Once cooled you don't want to keep it in the can either. Modern cans aren't made to do anything but store food, and should never be refrigerated once opened, as they can leach minerals from the tin into the food if your not careful. Just go with a steady heat, for at least two hours for your first time. Its the easiest dessert sauce I can think of, and a can of name brand sweetened condensed milk will set you back no more than 3 dollars.