Preheat oven to 325º. Grease and flour three 9" round cake pans. In a small bowl, stir together flour and next 7 ingredients. In a large mixing bowl, combine sugar, oil, wine, buttermilk, eggs and blackberry jam; mix well. Gradually add flour mixture to wet ingredients. Beat on low speed until blended. Scrape bowl, add vanilla and beat 4 minutes on medium speed. Stir in nuts if desired. Pour batter into prepared pan.
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center of the cake comes out clean. Let cool in pans on wire rack for 10 minutes. Remove to wire racks; cool completely.
Prepare blackberry wine filling.
1/3 c. sugar
3 T. cornstarch
2/3 c. Belle Meade Plantation Blackberry Wine
1/2 c. blackberry jam (seedless)
2 T. lemon juice
2 T. butter or margarine
Combine sugar and cornstarch in small saucepan. Stir in wine and blackberry jam; cook over medium heat, stirring constantly until thickened. Do not boil. Remove from heat; stir in lemon juice and butter. Cool completely.
Prepare blackberry wine frosting.
1/2 c. butter or margarine, softened
1/4 c. Belle Meade Blackberry Wine
4 c. (about 1 lb.) powered sugar
Beat butter and wine in medium bowl until creamy and well blended. Gradually beat in powdered sugar until smooth. Makes about 4 cups of frosting.
Place 1 cake layer on serving plate; top with blackberry wine filling. Top with second cake layer; top with blackberry wine filling. Add third layer; frost top and side of cake with blackberry wine frosting.