In a medium heavy-bottomed saucepan, whisk together the granulated sugar, all-purpose flour, and salt until evenly combined. Gradually pour in the whole milk, whisking constantly until the mixture is completely smooth with no lumps.

Heat the mixture over medium heat, stirring constantly, until it thickens and begins to bubble. Reduce heat and cook for an additional 2 minutes. Remove from heat.

Beat the egg yolks in a separate large bowl. Slowly ladle about ½ cup of the hot milk mixture into the yolks, whisking constantly to temper them. Add another ½ cup, still whisking, then pour the tempered yolk mixture back into the saucepan. Cook over low heat, stirring constantly with a whisk, until the custard thickens enough to coat the back of a spoon (about 2-3 minutes). Do not allow it to boil or the eggs will curdle.

Remove from heat and stir in the pure vanilla extract. Let cool slightly.

In a 2-quart trifle dish or 9x9 inch (23x23cm) serving dish, arrange a single layer of vanilla wafers across the bottom and slightly up the sides. Top with a layer of sliced bananas, then spoon about one-third of the warm custard over the bananas. Repeat the layers two more times, ending with a final layer of custard on top.

Press plastic wrap directly onto the surface of the custard to prevent a skin from forming. Refrigerate for at least 2 hours, or ideally overnight for the best texture.

Just before serving, whip the cold heavy cream to soft peaks and spread or dollop it over the top of the pudding. Garnish with lightly crushed vanilla wafers for texture contrast. Add the crushed wafers at the last moment — they go soggy within minutes.