Melt chocolate chips in small saucepan on low or in microwave, stirring in 15 second increments until smooth. Allow to cool.
In mixer, beat butter on medium until fluffy. Beat in sugar. Add cooled chocolate and vanilla.
Beating on high, add 1 egg at a time and beat each for 2 minutes. Mixture will become smooth and fluffy after final egg.
Pour into cooled crust and refrigerate for 2 hours.
In a mixing bowl or stand mixer fitted with the whisk attachment, beat heavy cream until stiff. Gradually add powdered sguar until just combined.
Refrigerate until ready to serve.
Refrigerate - Once the pie has chilled, cover it with plastic wrap and it will keep well for up to 3 days refrigerated.
Freeze - If you plan on freezing the pie, don't add the whipped cream. Add the filling to the pie crust and cover it with plastic wrap. It will keep well for up to 3 months this way. Thaw the pie in the fridge overnight and then top with the whipped cream and chocolate.