Melt half of chocolate (1/2 cup) in a medium heatproof bowl set over a medium pot of barely simmering water (bottom of bowl should not touch water), stirring occasionally, or in short bursts in the microwave, stirring in between bursts, until chocolate is melted and smooth
Using the back of a spoon, spread chocolate over bottom and sides of pie shell
Freeze until firm and dry, about 5 minutes
Cut ice cream pints in half with a serrated knife, remove packaging, then cut crosswise into 1" slices
Transfer to a medium bowl and let sit, stirring occasionally, until spreadable but not soupy, 5–10 minutes
Fill pie shell with ice cream; smooth top
Freeze until firm, about 1 hour
Melt remaining 1/2 cup chocolate in a medium heatproof bowl set over a medium pot of barely simmering water (bottom of bowl should not touch water), stirring occasionally, or in short bursts in the microwave, stirring in between bursts, until chocolate is melted and smooth
Using a fork, drizzle over pie
Freeze again until set, about 5 minutes
Transfer pie to a cutting board and let sit 10 minutes before slicing