In a small saucepan, melt chocolate chips with water; stir until smooth. Then, stir a small amount of hot chocolate mixture into egg yolk; return all to the pan, stirring constantly.
Cook and stir for 2 minutes or until slightly thickened.
Remove from the heat; and stir in the vanilla extract. Quickly transfer to a small bowl. Stir occasionally until completely cooled.
In a small bowl, beat whipping cream until it begins to thicken.
Then, add in sugar; beat until soft peaks form. Fold into cooled chocolate mixture.
Cover and refrigerate for at least 2 hours. If desired, garnish with whipped cream and raspberries.