In a heavy-bottomed pan, combine the butter, milk, salt, granulated white sugar, and brown sugar. Heat over medium heat, stirring constantly until the mixture comes to a boil.

Continue boiling and stirring for about 6 minutes to ensure the sugars dissolve and the mixture becomes smooth.

Remove the pan from the heat and let it cool slightly. Then, add the vanilla extract, unsweetened cocoa powder, and confectioners' sugar.

Beat the mixture using an electric mixer until it reaches a smooth, thick consistency.

Pour the fudge onto a buttered baking pan. Allow it to cool until it can be handled comfortably.

Use a spatula to shape the fudge into a log, then wrap it tightly in plastic wrap. Place the wrapped fudge in the freezer for 20 minutes to set.

Once set, slice the fudge into pieces of your desired size and serve. Enjoy!