In a medium saucepan, heat 2 cups milk to boiling.
While milk is heating, whisk
egg yolks, sugar and remaining 1/4 cup milk. whisk in cornstarch and flour until
Temper the egg mixture by slowly whisking in about 1/3 of the heated milk,
then whisking in remaining milk. Return mixture to saucepan and cook over medium-high
heat until mixture thickens and boils, whisking constantly. Reduce heat to low and
cook for another 2 minutes.
Remove from heat and stir in vanilla extract and melted chocolate. Pour into
a bowl, press plastic wrap on the surface to prevent a skin from forming and cool
to room temperature before chilling for at least 2 hours.