Drain both cans of pineapple, reserving 1 cup of the juice, and refrigerate the drained pineapple until assembly. Keep the fruit cold and well drained so it does not dilute the finished custard.

Whisk the reserved pineapple juice, granulated sugar, egg yolk, salt, and cornstarch in a saucepan over medium heat until smooth, then cook until it reaches a low boil and thickens slightly. The custard should look glossy and coat the back of a spoon like warm pudding before you take it off the heat to cool.

Cook the acini di pepe noodles according to the package directions, then drain and cool them completely. The pasta should be tender through the center, with separate pearls rather than a sticky clump.

Stir the cooled acini de pepe into the cooled pineapple custard in a covered container. Make sure the mixture is evenly coated, with no dry pockets of pasta remaining.

Refrigerate the pasta and custard mixture for a few hours or overnight, then transfer it to a large bowl and fold in the pineapple, mandarin oranges, coconut, mini marshmallows, and sliced banana. The chilled custard should look thicker and cling closely to the pasta before the fruit goes in.

Beat the heavy whipping cream and powdered sugar in a separate bowl until stiff peaks form, then fold the whipped cream into the salad. Stop folding when the mixture looks evenly fluffy and streak-free, without deflating the cream.