Preheat oven to 350 degree F. Lightly coat a 10-inch fluted tube pan with cooking spray; set aside. In a large bowl combine flour, granulated sugar, brown sugar, orange peel, lemon peel, snipped rosemary, baking soda, and salt.
In a medium bowl combine eggs, buttermilk, and butter. Add to flour mixture and stir just until combined. Spoon batter into prepared pan. Bake for 45 to 50 minutes or until a wooden toothpick inserted near the center comes out clean.
Cool in pan on wire rack for 15 minutes. Invert onto a serving platter. In a small bowl combine powdered sugar and enough orange juice to make a drizzling consistency. Drizzle over warm cake. Sprinkle with nuts. Serve warm. If desired, top with rosemary sprigs. Makes 12 servings.