You can add 1 to 2 tablespoons liqueur to any variation of this custard along with the vanilla if desired. For a lighter but richer filling, fold 1/4 to 3/4 cup Whipped Cream into this custard.
In a medium bowl, beat on high speed until thick and pale yellow, about 2 minutes:
      1/3 cup sugar
      2 tablespoons all-purpose flour
      2 tablespoons cornstarch
      4 large egg yolks
Meanwhile, combine in a medium stainless-steel or enamel saucepan and bring to a simmer:
      1 1/3 cups milk
      1 vanilla bean, split (optional)
Fish out the vanilla bean if you used it. Gradually pour about one-third of the hot milk into the egg mixture, stirring to combine. Scrape the egg mixture back into the pan and cook, whisking constantly and scraping the bottom and corners of the pan to prevent scorching, over low to medium heat until the custard is thickened and begins to bubble. Then continue to cook, whisking, for 45 to 60 seconds. Using a clean spatula, scrape the custard into a clean bowl. Stir in:
      1 to 2 tablespoons rum
      3/4 teaspoon vanilla (if not using the vanilla bean)
Cover the surface of the custard with a piece of wax or parchment paper to prevent a skin from forming. Let cool, then refrigerate. This keeps, refrigerated, for up to 2 days. Just before using, fold in:
      2 or more bananas, thinly sliced