Preheat oven to 350°.
Combine the first 4 ingredients in a small bowl, and stir well. Coat a 12-cup Bundt pan with cooking spray; sprinkle 1/3 cup of the walnut mixture into pan. Set walnut mixture aside.
Combine 1 1/4 cups sugar and vegetable oil in a large bowl, and beat at medium speed of a mixer until well-blended. Add eggs, 1 at a time, beating well after each addition.
Combine flour, baking powder, baking soda, and salt; stir well. Add flour mixture to creamed mixture alternately with buttermilk, beginning and ending with flour mixture; mix after each addition. Stir in vanilla.
Measure 2 cups of batter; set aside. Pour remaining batter into prepared pan; sprinkle remaining walnut mixture over batter. Pour reserved 2 cups batter over walnut mixture. Bake at 350° for 45 minutes or until a wooden pick inserted in center comes out clean. Let cool in pan 10 minutes on a wire rack; remove from pan. Let cool completely on wire rack.