Preheat oven to 350F. Grease four 6-inch cake pans and line bottoms with parchment paper. Set aside.
To prepare the banana cake layers, whisk together eggs, sugar, bananas and oil in a bowl, until mixture becomes smooth.
Sift in flour, baking soda, baking powder and salt. Stir until just combined.
Remove from oven and let rest for 10 minutes. Invert cake layers and place them on rack to cool.
To prepare ganache, place chocolate, heavy cream and corn syrup in a medium heatproof bowl over a pot of simmering water. Stir the mixture using a wooden spoon until melted and smooth, about 5 minutes. Remove from heat and let cool slightly.
To prepare buttercream frosting, place butter and powdered sugar in a mixing bowl. Beat until pale and fluffy, about 5 minutes. Add espresso and continue beating until well combined.
To assemble the cake, place one cake layer on a serving plate, spread 2 to 3 tablespoons ganache on top, followed by a layer of espresso buttercream. Continue until the last cake layer is placed. Frost the cake top and sides with the remaining buttercream. Garnish with chocolate sprinkles.
Cover and refrigerate the cake. Leave out in room temperature for at least an hour prior to serving.