Preheat oven to 350ºF (180ºC). Prepare 3 - 6" round pans. Use a pastry brush to apply Cake Release to the bottom and sides of pans. Wrap pans with dampened Wilton Bake Even Strips.
Using a whisk, combine flour, baking soda, baking powder and salt in a bowl.
In a separate bowl combine mashed bananas, buttermilk, and vanilla.
Add butter and sugar to the bowl of your stand mixer and using the paddle attachment, beat until light and fluffy.
Add the eggs one at a time and continue to beat. Scrape down the sides of the bowl as needed.
Add the flour mixture in thirds, alternating with the banana mixture - ⅓ flour mixture, ½ banana mixture - repeat, ending with the flour mixture. Beat until fully incorporated.
Divide the batter evenly between the three pans. I use my scale to help distribute the batter evenly among the pans.
Bake for 25-30 minutes, or until an inserted toothpick comes out clean.
Remove from the oven and allow the cakes to cool on racks for about 10-15 minutes. Invert on a wire rack to cool completely, if using immediately. Or wrap in plastic wrap while still warm, return to the pan and store in freezer until needed.
To make the sauce:
Place butter, brown sugar and heavy cream in a saucepan over medium heat. Stir until the mixture is smooth. Once it is smooth stop stirring. Let the mixture cook at a bubbling simmer for 3 minutes. Remove the mixture from the heat. Stir in the remaining cream. Let the mixture cool. Stir in vanilla extract. Store butterscotch in a mason jar in the refrigerator.
To make the frosting:
Using a clean towel and some lemon juice or vinegar, clean all equipment and utensils to be used for preparing the meringue.
Fill a heavy duty pot about a quarter of the way with water and place on the stove over medium heat to simmer.
Add egg whites, sugar and salt to the mixing bowl and use a hand whisk to combine. Attach a candy thermometer to the side of the bowl and place the bowl over the pot of water, ensuring the bottom of the bowl is not in contact with the water. Lightly whisk the sugar and egg white mixture constantly until temperature reaches 160°F. This took me about 12 minutes.
Once at the correct temperature, remove from heat, wipe away condensation from the bottom of the bowl with a towel and transfer mixing bowl to the stand mixer. be careful not to burn yourself.
With the whisk attachment and the mixer set to high (8-10), whip the meringue until it is thick, glossy and the bottom of the bowl is no longer warm to the touch. Do not begin adding butter while the bowl is still warm. This took about 10 minutes.
Switch from your whisk to paddle attachment and with mixer on low speed, add butter in small pieces until incorporated. Continue to mix until it has reached a silky smooth texture. This took approximately 12 minutes.
Add emulsion, vanilla beans and butterscotch sauce and continuing to beat on low speed until well combined. About 2-3 minutes.
Assembly: Center one layer of cake on a cake board of the same size, using a dab of buttercream. Spread a generous amount of buttercream on the top of the layer and add slices of banana on top of the buttercream. Pour a few spoonful of sauce over bananas and place another later of cake on top. Repeat for the next layer. Crumb coat the cake, cover and place in the fridge to set for fifteen minutes. Remove from fridge and frost with buttercream. Use a Wilton comb of your choice to decorate.