Make the caramel.  In a medium large saucepan stir together the sugar, syrup, and water over medium heat until sugar dissolves.  Raise heat to medium high and cook until mixture is bubbling vigorously with small bubbles, has thickened slightly, and is deep amber in color, but not burnt.  Remove from the heat and carefully stir in the butter and cream, replacing over the heat if necessary to emulsify the mixture.  Stir in the salt and vanilla bean scrapings and pod.  Pour into a heatproof bowl, cool to room temperature, cover and refrigerate.  Caramel may be stored in an airtight container in the refrigerator for up to 2 weeks.

Make the cake.  Preheat oven to 350 degrees F.  Oil two 8 inch round cake pans and line the bottom with parchment.

In a large bowl, whisk together the oils and sugars until well combined and slightly fluffy.  Beat in the eggs one at a time, followed by the vanilla and the banana.  Whisk in the flour and baking soda, followed by the milk until a batter forms.  Divide the batter equally between the pans.  Divide the caramel between the pans and swirl in using a butter knife or thin spatula.

Bake the cakes about 35 minutes until risen, golden brown, and a toothpick inserted in the center comes out clean or with a few crumbs.  Cool completely in pan before assembling.

When ready to assemble the cake, make the frosting.  Using a hand or stand mixer, beat the cream cheese and butter until light and fluffy and combined.  Beat in the maple syrup and vanilla.  Slowly beat in milk until a thick yet spreadable frosting forms.

Coarsely chop all but 10-12 of the nicest walnut halves.

Place one cake layer on the serving platter of your choice.  Top with frosting, a hearty sprinkle of walnuts, and a big drizzle of caramel.  Place the other cake on top.  Dollop remaining frosting on top of the cake, spreading over the top and down on the sides.  Dip reserved walnut halves in caramel and place on top of the cake.  Press remaining chopped walnuts onto the sides of the cake if desired.  Drizzle with caramel and chill at least two hours to set.

Cake may be stored in the refrigerator for up to 5 days.  Serve with additional caramel and a sprinkle of walnuts.