Add the milk and cream to a medium saucepan over medium heat. Bring to a simmer, stirring often.

In a medium bowl, whisk together the eggs, sugar, and cornstarch until well blended.

Spoon a little of the hot milk over the egg mixture and whisk well. Repeat with another few spoonfuls of the hot milk, to temper the eggs.

Pour the egg mixture into the saucepan and continue to cook over medium low heat for about 10 minutes or until it thickens.

Once thickened, remove from heat and stir in the butter, vanilla extract, banana extract, and salt.

Pour pudding through a sieve or fine mesh strainer into a container, to remove any lumps.

Place a piece of plastic wrap or wax paper directly on top to prevent a skin from forming. Refrigerate for at least 3 hours.

Preheat the oven to 325°F. Liberally spray 3 (8-inch) round cake pans with non-stick baking spray.

In your mixer bowl, add oil and butter and beat for 2 minutes on high speed. Slowly add in sugar and beat for an additional 4-5 minutes.

Add eggs, one at a time, combining well after each addition and scraping down the sides as needed.

Turn your mixer down to its lowest speed, and slowly add flour in two increments then add baking powder, salt, and baking soda.

Lastly, add sour cream, milk, vanilla extract, and banana extract, then mix until just combined.

Evenly pour cake batter into prepared baking pans and place in the oven to bake for 15-25 minutes.

Remove cakes from the oven and rest in pans for 10-15 minutes. Invert cakes and allow them to cool to room temperature.

Whip cream, sugar, vanilla, and cream of tartar until stiff peaks.

Chill until ready to use.

Place one layer of cake on a cake stand or serving plate. Spoon ½ of the banana pudding onto the cake.

Sprinkle crushed Nilla wafers on top.

Place the next layer of cake on top, then repeat the previous step.

Add the last layer of cake on top, then frost the cake with the premade whipped cream.

Decorate the top of the cake with Nilla wafers and slices of banana if desired.