Preheat oven to 325°. Beat butter at medium speed with a heavy-duty electric stand mixer until creamy. Gradually add sugar, beating at medium speed until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition.
Add flour to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Stir in vanilla. Pour batter into a greased and floured 10-inch (12-cup) tube pan.
Bake at 325° for 1 hour and 5 minutes to 1 hour and 10 minutes or until a long wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 to 15 minutes; remove from pan to wire rack, and cool completely (about 1 hour). Serve with Buttermilk Custard Sauce as desired.