Heat oven to 300℉/150℃.
In a medium bowl, combine egg yolks and sugar.
Beat with an electric mixer until light yellow and ribbony, about 3-4 minutes. Set aside.
Heat cream just until it starts to bubble around the edges.
Use a whisk to incorporate a small amount of hot cream into egg mixture.
Continue whisking in small amounts at a time until all cream is combined.
Add chocolate pieces.
Stir until chocolate is completely melted and mixed in.
Pour into individual ramekins, filling each about ¾ full.
Set in pan.
Boil enough water to fill the pan to halfway up the ramekins.
Set pan with ramekins on oven rack.
Pour boiling water in bottom of pan to halfway up the ramekins.
Bake for 30 minutes.
Remove from oven and carefully remove the ramekins from the water bath.
Allow to cool at room temperature.
Refrigerate until cold, about 2 hours.