Fill a medium bowl with ice water; set aside. In a small nonreactive saucepan, combine eggs, sugar, and passionfruit puree. Cook, stirring constantly, over medium-low heat until mixture thickens enough to coat the back of a spoon, about 3 minutes. Remove from heat, immediately add butter, and stir well to combine.
In a medium saucepan, combine the orange juice and 2 tablespoons cold water. Sprinkle gelatin over orange-juice mixture; let stand 5 minutes. Place over low heat until the gelatin is completely dissolved, about 2 minutes.
Pour passion-fruit mixture through a fine sieve or chinois into a non-reactive bowl. Stir in gelatin mixture. Place bowl over ice water; whisk constantly until the mixture has cooled.
In a chilled bowl, whip the heavy cream until stiff peaks form, about 3 minutes. Whisk one-third of the whipped cream into the passion-fruit mixture. Then, in two additions, fold the lightened passion-fruit mixture into the remaining whipped cream. Transfer mixture to a pastry bag fitted with a number 3 plain round tip; set aside.