3-Ingredient Frozen Mud Pie

["Preheat oven to 350u00b0F. Prick bottom of pie shell all over with a fork. Bake until golden brown and dry, 20-25 minutes. Let cool completely.", "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.", "Mousse can be made 2 days ahead; cover and chill."]