Butter an 8" square baking dish and line with a long sheet of parchment paper. Allow the long ends to stick up over two sides. These will be your handles to remove the fudge after it cools.
In a large saucepan, combine sugar, cocoa powder, evaporated milk and corn syrup. Put over medium heat and stir constantly until sugar dissolves.
Attach a candy thermometer or digital heat probe to the pan. Add 2 Tbsp butter to the pan and stir until melted. Bring to a boil and cook without stirring until thermometer reads 230 degrees. Remove from heat and add remaining butter, peanut butter and vanilla. Do not stir. Just let it sit for 10 minutes.
Transfer mixture to bowl of a stand mixer with the paddle attachment. Beat on medium speed about 3 minutes, until it thickens and looks less. Be careful not to overmix.
Pour into the prepared pan and smooth the top. If you like a little salt to go with your sweet, sprinkle a little coarse or Kosher salt on top of the fudge. Let come to room temperature then cover and refrigerate until cold. Pull the hardened fudge out of the pan using the “handles” and cut into 1" squares.
One Last Thing
If you have all your ingredients lined up and ready to go, this will be the quickest candy you’ll ever make!