1. Heat oven to 350°F. Grease and flour 12-cup fluted tube pan.
2. Beat butter, sugar, eggs and vanilla in large bowl until light and fluffy; stir in sour cream. Stir together flour, cocoa and salt. Stir baking soda into buttermilk in medium bowl; add alternately with dry ingredients to butter mixture. Beat 2 minutes on medium speed. Pour batter into prepared pan.
3. Bake 50 minutes or until wooden pick inserted into center comes out clean. Cool in pan 10 minutes. Remove from pan to wire rack. Cool completely. Glaze with ORANGE GLAZE; garnish as desired. 12 to 14 servings.
ORANGE GLAZE: Combine 2 cups powdered sugar, 1/4 cup (1/2 stick) melted butter or margarine, 3 tablespoons orange juice, 1 teaspoon vanilla extract and 1/2 teaspoon freshly grated orange peel in medium bowl; beat until smooth. About 1 cup glaze.
VANILLA GLAZE: Substitute 3 tablespoons water for orange juice and omit orange peel.
*To sour milk: Use 1 tablespoon white vinegar plus milk to equal 1 cup.