In a medium bowl, whisk cake flour, baking powder, and salt. Set aside
Using a stand mixer fitted with the paddle attachment, beat butter until smooth.
Add sugar and beat on medium-high until pale and fluffy, about 2-3 minutes.
Reduce speed and add eggs one at a time, fully incorporating after each addition. Add vanilla and mashed bananas and mix until well combined.
Alternate adding flour mixture and buttermilk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition. Do not overmix.
Spread batter evenly into prepared pans. Smooth the top with a spatula.
Bake for approximately 30 minutes or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10 minutes then turn out onto wire rack to cool completely.
Make the Buttercream Frosting:
Place egg whites and sugar into the bowl of a stand mixer*, whisk until combined.
Place bowl over a pan of simmering water to create a double-boiler. Whisking constantly, heat the egg mixture until it registers 160 degrees on a candy thermometer. Carefully transfer the bowl onto the stand mixer.
Using the whisk attachment, beat the egg white mixture on high speed for 8 to 10 minutes until the bowl is no longer warm to the touch and the meringue is fluffy, glossy and holds a stiff peak.
Switch to the paddle attachment. With the mixer on low, slowly add cubed butter and mix until incorporated.
Add vanilla and whip on medium-high until silky and smooth.
Make the Strawberry Sauce:
Place strawberries and sugar into a medium saucepan. Cook uncovered over medium-high heat, breaking down strawberries with a wooden spoon. Cook 5-10 minutes until softened and broken down. Cool completely before using.
Make the Pineapple Sauce:
Place all ingredients into a medium saucepan, stir to combine. Bring to a boil over medium-high heat. Cook 2-3 minutes until thickened. Cool completely before using.
Make the Chocolate Ganache:
Place chopped chocolate and cream into a microwave safe bowl. Stir to combine. Microwave for 20 seconds, stir. Microwave in 10 second intervals, stirring in between, until ganache is smooth and silky. Cool completely before using.
Assemble the Cake:
Cut each layer of cake in half horizontally.
Place one layer of the cake onto a cake stand or serving plate. Spread a thin layer of frosting and, using a large round tip, pipe a dam of frosting along the top to hold the filling. Place 3 tablespoons of strawberry sauce inside the dam and spread evenly.
Top with a second layer of cake. Spread approximately ½ cup of frosting on this second layer.
Top with a third layer of cake. Spread a thin layer of frosting and pipe a dam of frosting along the top to hold the filling. Place 3 tablespoons of pineapple filling inside the dam and spread evenly.
Top with a fourth layer of cake. Spread approximately ½ cup of frosting on this layer.
Repeat steps 2 & 3 and crumb coat the outside leaving the sides of the cake exposed. Use a bench scraper to smooth out the sides and top of the cake. Chill for 20 minutes.
Using a teaspoon, apply ganache near edges like so to create the drips like so. Pour some ganache to fill in the top of the cake and spread with an offset spatula.
Sprinkle some sprinkles along the top edge and sides of the cake.
When ready to serve, whip cream and sugar until thickened and pipeable. Fill a piping bag fitted with a large star tip.
Pipe rosettes of whipped cream and top with maraschino cherries.
For the frosting, ensure there is NO trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease free or your meringue may not stiffen.
Double check that your cake pans are 6 inch rounds. Using 8 inch pans will result in unusually short cake layers.