In a mixing bowl, cream shortening and sugars. Add eggs, one at a time, beating well after each addition. Beat in bananas and vanilla. Combine flour, baking soda and salt; add to creamed mixture alternately with buttermilk. Stir in nuts. Pour in a Pam sprayed 13 x 9 inch baking pan. Bake at 350 degrees for 25-30 minutes or until toothpick inserted near center comes out clean. Cool.
For frosting, combine brown sugar, butter and milk in saucepan. Bring to a boil over medium heat; boil and stir for 2 minutes. Remove from the heat; cool to lukewarm. Gradually beat in powdered sugar until frosting reaches spreading consistency. Frost the cake.