Caramel-Iced Blackberry Jam Cake

Prepare cake: Preheat oven to 350 degrees F. Grease two 10-in. round cake pans. Line bottoms of pans with parchment paper; grease parchment. In large bowl, whisk flour, baking powder, baking soda, salt, allspice, cinnamon, and nutmeg. In another large bowl, with mixer on medium-high speed, beat shortening and granulated sugar 5 minutes or until mixture is pale and fluffy. Add eggs, 1 at a time, beating well after each addition and scraping sides of bowl occasionally with rubber spatula. With mixer on low speed, beat in flour mixture alternately with buttermilk, beginning and ending with flour mixture, just until blended. With rubber spatula, stir in pecans and raisins, then stir in 2 cups jam until well blended. Divide batter evenly between prepared pans. Bake 50 minutes or until toothpick inserted in center comes out clean. Cool in pans on wire racks 10 minutes. Invert cakes onto racks, and remove and discard parchment. Cool completely on wire racks. Prepare filling and icing: Transfer 1 cake to cake plate, bottom side up. Spread 1 cup jam evenly over top, leaving 1/4-in. rim around edge. Place other cake, bottom side up, over jam. In 2-quart saucepan, melt butter on medium. Stir in brown sugar and heat to boiling. Reduce heat to low, and cook 2 minutes, stirring constantly. Add milk, and heat to boiling on medium, stirring constantly. Transfer to large bowl. With mixer on medium-high speed, beat in confectioners' sugar until smooth. Immediately pour over cake and, with butter knife, nudge icing over edge to create thick drips. Let stand to set icing. To serve, garnish cake with blackberries.