Melt the chopped chocolate in a double boiler, stirring until smooth.
In a large bowl, beat the softened butter and granulated sugar until light and fluffy.
Add the melted chocolate to the butter mixture and mix well.
Beat in the eggs, one at a time, ensuring each is fully incorporated.
Stir in the vanilla extract.
Pour the chocolate filling into the pre-baked pie crust.
Refrigerate the pie for at least 4 hours to set.
In a separate bowl, whip the heavy cream until soft peaks form.
Add the powdered sugar and continue whipping until firm peaks form.
Spread the whipped cream over the chilled pie before serving.