Grease and lightly flour two 9x1-1/2-inch round cake pans; set aside.
Combine buttermilk and soda; set aside. In a small bowl, mix flour and salt.
In a large mixing bowl, beat butter with electric mixer for 30 seconds. Add sugar; beat until well combined. Beat in eggs, one at a time, until combined. Beat in mashed banana and vanilla.
Add buttermilk mixture and flour mixture alternately to beaten mixture, beating on low speed after each addition until just combined. Pour into prepared cake pans.
Bake in a 350 degree F oven for 25 to 30 minutes or until a wooden toothpick inserted near center comes out clean. Cool in pans on wire racks for 10 minutes. Remove from pans. (Cool one layer thoroughly. Wrap and freeze for another time.)
For each serving, ladle 1/4 cup of the warm Butterscotch-Caramel Sauce onto a warm dessert plate. Slice the warm cake; place slices of cake on sauce. Top with banana slices, a scoop of ice cream, more sauce, and the pecans. Makes 10 servings.
Prepare the cake as directed. Remove layers from pans; cool thoroughly. Before serving, wrap a cake layer in foil. Warm in a 350 degree F oven for 15 minutes. Serve as directed.
To make sour milk, place 1-1/2 teaspoons lemon juice or vinegar in a glass measuring cup. Add enough milk to make 1/2 cup liquid; stir. Let stand for 5 minutes before using.
In a medium heavy skillet, combine brown sugar, corn syrup and butter. Cook and stir over medium heat until sugar dissolves and the sauce mixture begins to boil. Remove from heat; cool slightly. Stir in half-and-half or light cream. Serve the sauce warm. Makes 2-1/4 cups.