Prepare an 8x8 baking pan by greasing. You will use this later.
In a medium sized saucepan, add milk, cocoa, and sugar. Cook on medium/high stirring constantly. Bring mix to a boil, reduce heat and simmer. End stirring.
Use a candy thermometer, continue cooking until the temperature reaches 238° F.
Remove saucepan from the heat. Add in the butter and the vanilla. Using a wooden spoon, stir until the sheen goes away.
Pour the fudge into the prepared baking pan. After it cools, cut the fudge into approx. 1 inch pieces.