Bring the half-and-half to a simmer in a medium saucepan set over medium heat. Meanwhile, whisk the granulated sugar, cornstarch, vanilla, egg yolks and salt together in a medium bowl. Slowly whisk about 1 cup of the warm half-and-half into the egg mixture, then pour back into the saucepan, whisking constantly. Continue to cook over medium heat, whisking constantly, until mixture comes to a boil and thickens, about 5 minutes. Remove from heat and whisk in the butter.
Spread half the crushed cookies in the bottom of a 2-quart square or oval dish, top with half the pudding and half the banana slices. Repeat the layers ending with banana. Press a piece of plastic wrap directly against the banana slices and refrigerate until cold, about 30 minutes.
Whip the cream and confectioners? sugar in a large chilled bowl with an electric mixer on medium-high speed or by hand with a whisk until stiff peaks.
Spread the whipped cream over the pudding and refrigerate until the pudding is firm, at least 2 hours or overnight. Serve with crumbled wafer cookies on top.
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