Whip cream in a mixing bowl till stiff peaks form. Cover and chill.
Melt chopped chocolate in a glass bowl in the microwave at half power, stirring every 30 seconds till smooth. Set aside.
Place eggs, sugar, and water in a glass bowl or double boiler. Beat with an electric mixer for at least 5 minutes, or till very pale yellow and thick. Place bowl over a pot of simmering water that is slightly smaller than your bowl. You don't want it to touch the water. Cook and whisk till mixture reaches 160°.
Remove egg mixture from heat. Beat for another 8 minutes or till cooled and fluffy. Don't under-mix!!
Add melted chocolate and vanilla and beat till smooth. Beat in the soft butter, then fold in the whipped cream. Pour mixture into the pie crust and spread evenly.
Beat the 1/2 cup cream till soft peaks form. Add the powdered sugar and vanilla and beat till smooth. Spread over the chocolate filling. Cover and chill for at least 2 hours.
Just before serving, garnish with chocolate curls or shavings.