Break the corn starch biscuits into small pieces and set them aside.
In a bowl, place the condensed milk, the melted butter and the cocoa powder, mix it all together very well until a mixture is formed. Transfer this mixture to the bowl with the broken biscuits and mix very well with a spoon.
Place all this mixture over a plastic bag or plastic wrap. Roll it into a log shape, squeezing well. Roll up the tips of the plastic bag and take it to the fridge, leave it there for at least 3 hours.
Take it out of the fridge and unwrap it gently. Sprinkle some milk powder or icing sugar over the chocolate salami, but that's totally optional. Cut it into round slices.
Serve.