Melt chocolate and butter in microwave. Set aside.
Mix cornstarch, sugar and salt together, stir in 1/4 c. evap milk then add the melted chocolate and blend. Stir in remaining milk and water and cook in microwave for approx. 10 min on high. Stopping to stir at 5 min. then every 2 min. so cornstarch does not clump. Add vanilla and pour into cups. Chill. Makes great pie filling also.