Preheat oven to 350° F. Grease and flour lightly a 9" x 9" x 2" baking pan. Set aside.
In a large mixing bowl, cream together, sugar and butter; beat in eggs. In a separate bowl, stir together flour and spices; add alternately with buttermilk, beating until well blended after each addition. Fold in blackberry jam and nuts leaving swirls of jam. (Do not overmix) Turn into prepared pan and bake for 25 minutes or until toothpick inserted in center comes out clean. Cool Completely. Frost with Caramel Icing
In a small saucepan, melt butter; stir in brown sugar. Cook stirring constantly until mixture bubbles; remove from heat. Cool 5 minutes. Stir in milk and blend in powdered sugar; beat until spreading consistency is reached.