In a large saucepan over medium-low heat, mix together the chocolate, milk, coconut oil or butter, vanilla extract and salt. Stir until melted and completely smooth.
3 cups (510 grams) semi-sweet chocolate, 3/4 cup (180 ml) milk of choice, 3/4 cup (168 grams) refined coconut oil, 1 tablespoon vanilla extract, 1/4 teaspoon salt
Let the pan cool for about 15 minutes (or until cool enough to place in the refrigerator) and then place the pan in the refrigerator for about 1-2 hours, stirring after every 15-20 minutes, or until firm enough to spread on the cake. I usually need about 1 hour. If you forget about it and leave it in the refrigerator for too long, it'll be too firm to spread on the cake, so be sure to keep checking on it. If it gets too hard, very lightly reheat it on low heat, while stirring constantly, until it's soft enough to spread.
Once the cake has cooled, spread about 3/4 cup of frosting on the first layer, about 1 cup on top of the cake, and the rest on the sides. If you have any left over, it freezes great.
Cover and refrigerate leftovers for up to 4 days. You can also freeze the frosted cake or unfrosted layers for up to 3 months.