Do you mean using sweetened condensed milk as opposed to evaporated milk and sugar? If so, you want to cook the condensed milk until it reaches softball stage 237 – 239F (114 – 115C) on a medium low heat, stirring constantly and adjusting the temperature down as needed to prevent burning. You really have to make sure to really keep that mixture moving or you will scorch the condensed milk quite easily. You add in the remaining ingredients as described in the recipe.