Take a large mixing bowl and mix cocoa, sugar, and salt together.
Add milk to it gradually and mix thoroughly and bring it to bubbly. Boil the mixture on high heat and stir it continuously.
After some time, reduce the heat to a medium temperature and without stirring, continue to boil for about 20 minutes.
Remove the saucepan from heat and add butter and vanilla to it but do not stir the mixture.
Then allow it to cool at room temperature until the mixture attains the temperature of 110 degrees.
Now stir it by hand until the fudge loses some of its gloss.
Grease an 8x8x2 pan and pour the mixture in it quickly and spread it evenly.
Allow the mixture to cool and then cut into square pieces.
The cocoa fudge is ready.
