Take a small bowl and add the cocoa powder, wheat starch, and sugar. Mix everything well.
Mix the whole milk and cream in a measuring cup. Take about 50 ml (or 6 tablespoons) of it and stir this amount into the cocoa powder mixture until no lumps are visible.
Place a serving bowl or several small bowls, where the pudding will go later, in the fridge so they are nice and cold.