To make the passionfruit custard, bring the milk to a simmer in
a saucepan over medium heat. Meanwhile, whisk the egg yolks, sugar, and flour in a bowl. Gradually whisk the hot milk into the egg mixture until well combined. Return to a clean saucepan over medium heat. Cook, stirring, for 5 mins or until the custard boils and thickens. Remove from heat. Stir in the passionfruit pulp. Cover the surface of the custard with a disc of baking paper.
Set aside to cool completely. Place in the fridge for 2 hours to chill.
Use an electric mixer to whisk the passionfruit custard and cream in a bowl until smooth.
Use half the cake to line the bases of 8 serving glasses. Drizzle with half the rum. Reserve some of the mango for serving. Top the cake with half the remaining mango, then half the custard mixture. Repeat with the remaining cake, rum, mango, and custard mixture. Top with extra cream and reserved mango.