Put stevia and cocoa powder into a bowl and mix.
Pour milk into a saucepan and heat over low heat.
Add the mixed powder to the warmed milk and stir until dissolved.
Simmer and stir over low heat until the mixture thickens.
Pour into a small mold or container, cool, then let it set in the refrigerator for at least 1 hour.
Take out the set fudge and cut into bite-sized pieces.