Instructions. 1  Mix sugar and milk together in a heavy-bottomed saucepan. 2  The goal is to reduce the quantity in the pot (which is now about 1Â¾ cups) by approximately half. 3  Once reduced to your satisfaction, whisk in the butter and vanilla. The recipe is equivalent to just less than one whole can of brand name sweetened condensed milk. (One can = 14 ounces, which is 2 ounces shy of 2 cups. by weight, oops! The can is equal to 1Â¼ cups liquid. Substitute tables for homemade condensed milk vary from 1Â¼ cups all the way to 2 cups.