1Preheat oven to 350 degrees F. Grease a 13x9-inch cake pan and put aside.
2Make crumb topping by blending with a fork the butter into the sugar and spices and slowing mixing into the wafer crumbs. Stir in the granola and walnuts. I find it easily, and faster, to mix this with my hands incorporating all together uniformly. Put aside.
3Mix the flour, leavening, salt and oats together in a bowl, put aside.
4In a large mixing bowl, cream the sugar and butter until light and fluffy. Beat in eggs one at a time mixing well. Beat in the vanilla. Mix in order the flour, buttermilk and mashed bananas alternating in three intervals. Scrape down the sides of the bowl during the last addition. Fold in the coconut with a spatula.
5Spread the batter into the prepared pan, even out with the spatula and sprinkle the crumb topping on top. Even out the topping and lightly press down a bit forcing some into the cake batter.
Bake in the oven for 35 to 40 minutes or until center tests done. (I still use a wooden skewer for the test) Remove from oven and let cool about 20 minutes before serving.
6Caramel sauce :
In a small heavy saucepan over medium heat, combine sugar, butter, cream and salt. Bring to a boil and cook for 1 minute.
Remove from heat and stir in the water and cognac until smooth. Serve slightly warm or at room temperature.