Preheat the oven to 350 degrees F (180 degrees C). Line a 9x9-inch square pan with enough parchment paper to have overhang on all sides.

Mix together vanilla wafer crumbs and salt until combined. Add melted butter and mix until crumbs are thoroughly moistened. Pour mixture into the prepared pan and press firmly and evenly into the bottom of the pan.

Bake crust in the preheated oven until slightly browned, 12 to 15 minutes. Remove crust from the oven and cool for 5 minutes. Leave the oven on.

Meanwhile, for filling, place bananas, sweetened condensed milk, half-and-half, eggs, egg yolk, cornstarch, vanilla, lemon juice, nutmeg, and salt into the cup of a high-speed blender. Blend on high speed until mixture is smooth and combined, about 1 minute. If desired, pour mixture through a fine mesh strainer to ensure no lumps remain.

Pour banana filling over crust.

Return pan to the oven and bake until filling is set, 30 to 35 minutes. Remove from the oven, and allow the bars to cool completely in the pan, about 1 hour.

For whipped cream topping,  place heavy cream, confectioner’s sugar, vanilla, and salt in a large bowl. Beat mixture on medium-high speed until it holds stiff peaks. Spread whipped cream evenly over the cooled bars. Refrigerate bars for at least 2 hours.

When ready to serve, carefully lift bars out of the pan using the parchment overhang. Cut into 16 bars. Top each bar with extra banana slices and vanilla wafers, if desired. Store bars in the refrigerator.