In a small pan, heat the condensed milk and butter over medium-low heat, stirring constantly for about 20 minutes. You want your milk to thicken and slightly caramelize, but not stick to the bottom of your pan or turn into dulce de leche.
Remove from the heat and add 100g/3.5 oz. coconut. Mix well.
Allow to cool slightly before forming truffle-sized balls. You’ll need your mix to still be on the warm side to form the balls because once it’s cooled, it solidifies and is difficult to work with.