Preheat your oven to 350 degrees, and grease 3 8-inch round cake pans. Set aside.
In a large bowl, beat together the butter, brown sugar, and sugar until smooth. Add in the eggs, one at a time. Then, beat in the mashed bananas and vanilla extract.
In a medium bowl, stir together the flour, almond flour, salt, cinnamon, and baking soda. Beat the flour mixture into the butter mixture in parts, alternating with the buttermilk. You want to start and end the process with the flour mixture. Beat until the batter is completely incorporated, about 1-2 minutes.
Divide your batter evenly into your prepared baking pans. Bake for 30-35 minutes, or until a cake tester comes out clean. Cool in the pans for 15-20 minutes.
Gently turn the cakes out onto plastic wrap, and wrap tightly. Chill for 30 minutes to an hour.
Once the cakes have chilled, trim the tops to make a flat surface. I find this is easiest with a large, sharp knife.
Preheat your oven to 300 degrees, and line a baking sheet with parchment paper. Crumble your trimmed excess cake onto the sheet pan, and spread evenly. It does not have to be perfect. Bake for 15-20 minutes, or until the cake crumbs have started to become a dark golden brown. Cool completely on the sheet pan, and then crush to a fine crumb.
In a large bowl over a double-broiler, whisk together the egg whites and sugar, and cook until the sugar has dissolved. The mixture should be at about 150 degrees.
Remove from the heat, and beat the mixture on medium speed until stiff peaks form. This will take about 10 minutes with a stand mixer, and a bit longer with a hand mixer.
Slowly beat in your softened butter. The mixture will become thin, and then it will look separated- keep beating. After 10-15 minutes of mixing, your frosting should come together into a smooth mixture.
Beat in the salt, vanilla extract, melted chocolate, and cocoa powder until completely combined. Frost your cake as desired, using the toasted cake crumbs as a coating for the outside!