Preheat an oven to 350 degrees F. Butter a 12 by 17 inch jelly pan / baking pan. Line the pan with parchment or wax paper (optional), then butter and flour the paper (flour the pan if no paper is used).
To make the cake: In a small bowl, whisk together the flour, baking soda and salt.
In a large bowl, cream the butter and sugar with an electric mixer. Add the eggs one at a time, beating well after each addition.
Beat in the mashed bananas and the vanilla.
Beat in the flour mixture and the chocolate chips until smooth.
Pour the batter into the prepared pan and bake for 20-25 minutes or until the centre is set. Cool on a rack.
Loosen the cake with a spatula and carefully invert onto a large piece of foil.
Cut the cake into half, trimming off the edges.
For the Ganache: In a medium saucepan, bring the cream to a simmer. Remove from the heat and stir in the sour cream. Pour the mixture over the chocolate in a medium bowl, then stir until smooth. Refrigerate until the filling firms up but is still spreadable.
Spread the Ganache filling over the cake layer. Slice the 2 whole bananas to discs and arrange evenly over the Ganache. Place the second cake layer on the top.
To make the glaze: In a heavy saucepan, bring the cream to a simmer. Remove from the heat and stir in the butter and chocolate. Stir until smooth.
Pour the warm glaze over the cake and smoothen, allowing it to run down the sides. Place the cake in the freezer for 30 minutes. Cut the cake into slices, let sit at room temperature for 15 minutes before serving.