The dulce de leche people know of in the US is either the pasty Argentinian version or simply caramel with a fancier name, most likely swirled in vanilla ice cream. There is nothing wrong with these, but what I grew up knowing by that name is something totally different. It might have the same ingredients, sugar and milk, but the addition of one key ingredient makes all the difference: rennet.
To make it, simply warm 2 gallons of whole milk (you can also add a few cups of heavy cream) and one rennet pill in a huge pot, very slowly until the cream separates from the water.This process was done at room temperature by my grandmother (which is about 85 degrees and 80% humidity in Puerto Rico, by the way) but I find using the stove a much quicker process. Strain most of the water out (at least half), reserving it just in case it dries out during cooking, add 5 lb bag of sugar, and cook on low medium heat without stirring much until you see what's on the picture. It takes several hours (4-6) to make so get a bottle of wine, a good movie, and relax.