Mix sugar and flour in a saucepan. Separate eggs. Reserve whites for meringue. Stir yolks with a fork until blended. Add milk in same cup as egg yolks. Slowly stir egg/milk mixture into sugar/flour mixture until well blended. Bring to a boil over medium heat, stirring constantly. Cook for 3 to 4 minutes, until very thick. Remove thickened custard from heat, add butter and allow to melt. Cool. Add vanilla flavoring.
Divide half of the crushed wafers between 4 (8-ounce) glasses or goblets. Top each with 5 to 6 slices banana. Pour half of the cooled custard evenly into each glass over the bananas. Repeat each layer with the remaining ingredients. Refrigerate until ready to serve.
To make the meringue: whisk together the reserved egg whites and sugar in a large heatproof bowl. Set the bowl over a saucepan of gently simmering water and whisk constantly until the sugar is dissolved and whites are very hot to the touch. Transfer the mixture to the bowl of a standing mixer. Whip the whites until stiff, glossy peaks form and the meringue is cool. Add the vanilla and mix well. Spoon the meringue or pipe with a piping bag over the pudding in each glass.
Using a hand-held blowtorch, brown the meringue until golden. Serve immediately.
Adapted from Hazel Smith-World's Best Banana Pudding Recipe