Take an 8-inch square pan and lightly butter it. Set it aside.

In a large saucepan, mix together the cocoa powder, sugar, and salt. Stir to combine thoroughly.

Add the milk and butter to the saucepan and stir to combine.

Place the saucepan on medium heat and bring the mixture to a boil. Make sure to stir the mixture constantly.

Let the mixture boil for about 3 minutes. Keep stirring it to ensure that the mixture doesn't stick to the bottom of the saucepan.

Remove the saucepan from the heat and add the vanilla extract. Stir well to combine.

Using an electric mixer, beat the mixture for about 5 minutes, until it starts to thicken and lose its shine.

Pour the mixture into the prepared pan and smooth it out with a spatula.

Place the pan in the refrigerator and let the fudge chill for about 2 hours.

Remove the fudge from the pan and cut it into small squares. Serve and enjoy!