200gsugar or sugar substitute equivalent to 1 cup sugar, stevia or 1 1/2 cup Splenda or some other sweetener
In a heavy-bottomed (9 inch, 24 cm) pan, bring the milk to a boil over medium-low heat.
Put the heat as low as it can go and simmer (stirring often to keep the milk from burning) for about 1 hour and 15 minutes (if you use smaller pan or pot you will need to cook longer). The goal is to reduce the quantity of milk by approximately 60 %.
This is your sugar free evaporated milk. To make condensed milk, at this point add your sugar substitute of choice, vanilla extract and butter. Remove from heat and let cool before using. The mixture will thicken some more after it has cooled.