Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan, two 9-inch round cake pans, or three 8-inch round cake pans.
In a large bowl, combine cake flour, sugar, baking soda and salt. Mix in butter, shortening, buttermilk, eggs, raisins, nuts, orange zest and vanilla. Beat with an electric mixer for 3 minutes on high speed. Pour batter into prepared pan.
Bake in preheated oven until a toothpick inserted in center of cake comes out clean. Bake 9x13 inch pan 45 to 50 minutes, or layers 30 to 35 minutes. Allow to cool, and frost with Williamsburg Butter Frosting.