Step 1

Whip cream: With electric mixer on medium-high speed, whip cream to stiff peaks, 2 to 3 minutes. Transfer whipped cream to small bowl and refrigerate.

Step 2

Beat eggs: Combine eggs, sugar, and water in large heatproof bowl set over medium saucepan filled with ½ inch barely simmering water (don’t let bowl touch water). With electric mixer on medium speed, beat until egg mixture is thickened and registers 160 degrees, 7 to 10 minutes. Remove bowl from heat and continue to beat egg mixture until fluffy and cooled to room temperature, about 8 minutes.

Step 3

Beat, fold, cool: Add chocolate and vanilla to cool egg mixture and beat until incorporated. Beat in butter, a few pieces at a time, until well combined. Using spatula, fold in whipped cream until no streaks of white remain. Scrape filling into pie shell and refrigerate until set, at least 3 hours and up to 24 hours. Serve.