Pour half and half into a large saucepan, add seeds of vanilla bean and the vanilla bean pod, and nutmeg to the half and half. Heat over medium heat until it is just simmering.

Meanwhile, whisk together 3/4 cup sugar, cornstarch, salt, and egg yolks until slightly pale and fluffy, about 1 minute.

Once half and half is simmering, slowly pour 1 cup hot half and half into the sugar egg yolk mixture while whisking. Then pour that mixture into the saucepan while whisking vigorously.

Cook and whisk vigorously until thickened and large bubbles appear, then cook and whisk 30 seconds longer.

Immediately pour and scrape mixture into a heatproof bowl. Add butter and stir mixture well. If using vanilla extract, add it now and stir in.

Cover with plastic wrap, clinging to the top of the pudding to prevent skin from forming, and chill for 2 hours or until cooled.

Align 30 vanilla wafer cookies into the bottom of an 8 by 8 by 2-inch baking dish, slightly overlapping them.

Remove vanilla bean from pudding and dollop half of the pudding over the cookies in spoonfuls, then spread evenly. Slice 2 of the bananas into 1/4-inch thick slices and align evenly over pudding layer, brushing top of bananas lightly with lemon juice.

Align 30 more vanilla wafer cookies over banana layer, followed by spreading over remaining half of the pudding.

Cover and chill for at least 2 hours.

In a mixing bowl, using an electric hand mixer, whip together heavy cream, 2 Tbsp granulated sugar, and 1/2 tsp vanilla on medium speed until it thickens, then increase to high and whip until very stiff peaks form.

Cut remaining 2 bananas into 1/4-inch slices. Spread slices evenly over pudding layer, then brush with lemon juice.

Spread whipped topping evenly over bananas. Garnish with some of the remaining cookies, slightly crushed and some banana slices just before serving to prevent browning.