Prepare the instant pudding according to package directions, whisking in the milk and allowing it to set in the refrigerator until cold. Add vanilla extract to the pudding and stir to combine. One cup of prepared pudding is approximately half of a standard pudding box.

Lightly spray a 9x5 inch loaf pan with nonstick spray and line with plastic wrap, leaving overhang on all sides. The spray helps the plastic wrap cling to the pan walls for a smooth, wrinkle-free lining.

In the bowl of a stand mixer fitted with the whisk attachment, combine heavy cream, confectioner's sugar, and vanilla extract. Whip to medium-stiff peaks.

Reserve about one cup of whipped cream for the topping and set it aside. Gently fold the remaining whipped cream into the chilled pudding until combined.

Slice the bananas to about 1/8 inch thick. Starting with the lightened pudding, spread a thin layer across the bottom of the prepared pan, then layer on bananas and Nilla wafers. Repeat until the pan is almost full.

Spread the reserved plain whipped cream over the top. Decorate with additional Nilla wafers or banana slices, or leave it plain.

Cover tightly with plastic wrap and freeze for at least 8 hours or overnight.

When ready to serve, allow the cake to sit at room temperature for 5 minutes. Fill a large cup with hot water and have a tea towel nearby. Gently pull the plastic wrap overhang to release the cake from the pan, then remove the plastic wrap completely.

Dip a serrated knife in the hot water, wipe the blade dry, and slice the cake. Repeat between cuts, and return the cake to the freezer briefly if it begins to soften before slicing is complete.