Sift together cocoa and sugar.
In a heavy-bottom saucepan over medium heat, warm milk until just barely simmering.
Whisk in cocoa mixture until smooth.
Add chocolate and stir until chocolate is melted and mixture is smooth and glossy.
You can add additional milk to get the desired smoothness if it’s too thick.
Transfer mixture to a fondue pot and serve immediately with fruit such as strawberries, dried apricots and pineapple chunks for dipping.