This recipe is a combination of my Aunt Veronica Downeys cake and my Great Grandmothers. It is over a 100 years old. Aunt Ronnie made homemade blackberry jam every summer and this was the cake she had waiting for me when I came home every summer.
Cream butter and sugar until creamy and sugar is dissolved. Add eggs,one at a time and beat after each addition. Mix dry ingredients together and then add alternately with buttermilk. Stir in jam by hand until mixed well. Bake in three, greased, floured, 9 inch pans in a 350 oven for 20 to 30 minutes. Remove from pan and cool on cake racks for five minutes. Turn onto wax paper, poke holes with a toothpick all over top of each layer. Pour warm filling over cake top and allow to cool.
Prepare filling while cake bakes. Combine butter, brown sugar and buttermilk. Cook and stir over medium heat for 3 to 5 minutes. Remove from heat and stir in vanilla. Spread 1/3 of filling on top of each cake layer.
Cook first three ingredients of fruit filling together to soft ball stage. Remove from heat. Beat with mixer until thick and cool. Add remaining ingredients and mix well. Spread between cake layers and then frost.
Combine buttermilk, sugars and soda in large saucepan. Cook to soft ball stage (will hold its shape). Add butter and remove from heat. cool five minutes. Add vanilla and beat until thick and creamy with a mixer. If frosting is too thick add a small amount of cream. Frost cake.