1. Heat oven to 325°F. Grease and flour 12-cup fluted tube pan or 10-inch tube pan.
2. Beat butter, sugar and vanilla in large bowl 3 minutes on medium speed of mixer. Add eggs, one at a time, beating well after each addition. Stir together flour, cocoa, baking powder and salt; add alternately with buttermilk to butter mixture, beating well just until blended. Pour into prepared pan.
3. Bake 1 hour and 20 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes; remove from pan. Cool completely.
4. Sprinkle with powdered sugar or glaze with VANILLA GLAZE or BUTTER RUM GLAZE. Garnish with pecans or walnut halves, if desired.
VANILLA GLAZE: Melt 1/3 cup butter or margarine in small saucepan. Remove from heat; stir in 2 cups powdered sugar and 1-1/2 teaspoons vanilla extract. Add 2 to 3 tablespoons water, 1 tablespoon at a time, beating with whisk until glaze is of desired consistency. Spoon onto cake allowing some to drizzle down sides.
BUTTER RUM GLAZE: Omit vanilla; substitute 2 tablespoons light rum or 1 teaspoon rum flavoring. Stir in hot water, 1 teaspoon at a time, until glaze is of desired consistency.
* Use 1 tablespoon and 1-1/2 teaspoons white vinegar plus milk to equal 1-1/2 cups.
NOTE: Two 9x5x3-inch loaf pans may be substituted for tube pan. Bake at 350°F. 1 hour and 10 minutes.