This sour milk dessert was my mother's solution to a common occurrence in my family. Just as you "made lemonade out of lemons" in my house leche cortada(literally, cut milk) would be saved from going down the drain by being converted into this tasty dessert. It is quite a common dessert in the Hispanic Caribbean
My mother would use whatever amounts of soured milk was on hand and instinctively adjust the proportions of the rest of the ingredients. Milk in my house does not last long enough to sour and I could never improvise like she could so I sour my own milk by mixing in the lemon juice into it. After a half hour or so, the milk will get lumpy. When it does, mix all the ingredients in a pot and cook at a simmer. Don't stir the mixture unless it starts to adhere to the bottom of the pot. Let it boil until the milk firms up, gets granular and floats in the light caramel that forms. Refrigerate until cold and serve.