Line an 8 x 8-inch square pan with parchment paper and set aside. Mix together the butter, milk, salt, and brown and white sugars in a heavy saucepan and bring to a boil over medium heat. Boil and stir continuously for 6 minutes.

Then remove the mixture from the heat and stir in vanilla, cocoa powder, and confectioner's sugar. Stir until well combined and the fudge is smooth and shiny.

Pour the mixture into your 8 x 8-inch prepared pan and let cool completely.

Once the fudge is cool to the touch, with a spatula roll it into log form, wrap it in clingfilm, and place it in the freezer for 20 minutes.

Once completely set, cut the fudge into small squares and enjoy!