Butter an 8x8 or similar baking dish and set aside.
In a medium saucepan, whisk together the sugar and cocoa powder.
Add the butter and evaporated milk to the saucepan. Stir over medium heat until the mixture comes to a full rolling boil.
Once boiling, begin timing and continue stirring constantly for 7 minutes.
Remove from heat and stir in the vanilla extract (and nuts, if using).
Continue stirring for 3 minutes, then quickly pour the fudge into the prepared dish.
Let cool completely until set before cutting into squares.
