Hi, I'm a pastry chef from Argentina and DDL we use for comercial use, such as filling cake and alfajores (two cokkies filled with DDL), a thicker one that you can't make it at home. You can try to keep it cooking until Dulce de leche 2 lt de whole milk 700 g sugar 300 g liquid glucose 1 vainilla seed 1/2 teaspoon of baking soda Baking soda prevents from cristalization of sugar. The colour of the DDL is from the sugar (Maillard reaction). Procedure Put in a pan the milk, sugar, glucose an vanilla seed opened. Put in low heat and let it boil for one hour, here in argentina we use little balls of glass, that we put inside the pan and when al the mixture boils, they kept from the sugar and milk burn in the bottom. You can remove it with a wood spatula or spoon When the hour has passed, add the baking soda. Continue cooking it for 30 or 60 minutes more, and removing from time to time. To recognize when it's done you have to put a small portion in a small plate and move the plate, if it slides hardly, it's done, if not keep on boiling. Remove from heat and put inside esterilized glass jar. Let it cool and put in fridge. I think this DDL should work for filling cakes. Sorry for my english.