Start by mixing in a bowl the corn flour with the 2 tbsp. milk. We want the corn flour to melt completely and not have pieces in the milk.
Pour the chocolate into a saucepan. Add the cocoa and sugar substitute. Pour the milk and salt. Stir it up.
As soon as it starts to boil, pour the corn flour-milk mixture. Stir until the chocolate starts to set.
You have to drink it hot as it solidifies more and more as it cools.