We can't decide what's better about this pie: its 5-star taste or its cost per serving. Or just the chocolate. That's good, too.
Prepare crumb crust. Then combine first 6 ingredients in a medium saucepan, whisking well. Bring to a boil over medium heat, whisk constantly for 8 minutes. Remove from heat.
Stir in chocolate until smooth. Stir in butter and vanilla. Pour into pastry shell. Cover top of tart with wax paper. Chill at least 3 hours.
Whip cream and sugar until stiff. Spoon on top of tart.
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