In a pan, add the condensed milk and the cocoa powder and mix until combined.
Now, take the pan to the heat, over medium-low.
Stir the mixture nonstop until it cooks through and begins to release from the bottom of the pan.
Now, add the butter and keep stirring until the mixture gets thicker, like a sticky fudge.
After that, transfer this mixture to a small dish lined with plastic wrap and spread it evenly until flat.
Take it to the fridge and let it chill for 2 hours.
After this indicated time, sprinkle cocoa powder over a cutting board.
Unmold the fudge over this cocoa powder, sprinkle more cocoa powder all over it and cut it into equal-sized pieces.
Serve.