1. Preheat oven to 350°.
2. Place granulated sugar, 6 tablespoons butter, and oil in a large bowl; beat with a mixer at medium speed until well blended (about 5 minutes). Add eggs, 1 at a time, beating well after each addition. Beat in 1 tablespoon lemon rind, 2 tablespoons lemon juice, and vanilla. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 4 ingredients (through salt), stirring well with a whisk. Add flour mixture and buttermilk alternately to sugar mixture, beginning and ending with flour mixture.
3. Spoon batter into 12-cup Bundt pan coated with baking spray. Bake at 350° for 38 to 40 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 15 minutes on a wire rack; remove from pan. Invert cake onto a plate.
4. To prepare glaze, combine 1 tablespoon butter, powdered sugar, and 3 teaspoons lemon juice in a medium bowl; stir until smooth, adding remaining 1 teaspoon lemon juice, if necessary, to reach drizzling consistency.
5. Spoon glaze over cake. Sprinkle with grated lemon rind, if desired. Cool completely before slicing.