If you don't have sweetened condensed milk on hand or the dry milk powder stuff, here is an alternative substitute.
One cup evaporated milk in a saucepan over medium heat. Add 1 1/4 cup sugar. Stir until dissolved. Let cool.
That "let cool" part. It's important. But otherwise this substitution worked like a gem for my cookies yesterday.
Who knew there was SO MUCH sugar in sweetened condensed milk?! Oh my!