Combine the first 4 ingredients in a bowl; let stand for 30 minutes. Drain and set aside.
Preheat oven to 375°.
Lightly spoon flour into dry measuring cups, and level with a knife. Combine flour and next 4 ingredients (flour through baking soda) in a large bowl; cut in butter with a pastry blender or 2 knives until the mixture resembles coarse meal. (Flour mixture and butter can also be combined in a food processor; pulse until the mixture resembles coarse meal.) Add reserved fruit; toss well to combine. Make a well in center of mixture. Combine the buttermilk, orange rind, lemon rind, and egg in a bowl, and stir with a whisk. Add to flour mixture. Stir just until moist. Let stand 2 minutes.
Turn dough out onto a lightly floured surface; knead lightly for 1 minute with floured hands. Divide the dough in half; shape each half into an 8 x 4-inch oval loaf. Place the loaves on a baking sheet coated with cooking spray and sprinkled with cornmeal. Make 1 lengthwise cut 3/4-inch-deep across the top of each loaf using a sharp knife. Brush the loaves with 2 teaspoons milk; sprinkle with 1 tablespoon sugar. Bake at 375° for 30 minutes. Reduce the oven temperature to 350° (do not remove the bread from oven); bake an additional 25 minutes or until loaves are browned on the bottom and sound hollow when tapped. Remove the loaves from pan, and cool on a wire rack.