Preheat oven to 450°.
Coat a 13 x 9-inch baking pan with cooking spray, and dust with 1 tablespoon flour.
Place sugar and butter in a bowl; beat with a mixer at medium speed until well blended. Add eggs, 1 at a time, beating well after each addition. Stir in buttermilk. Lightly spoon 1 cup flour into a dry measuring cup; level with a knife. Combine flour, cornmeal, baking powder, baking soda, and salt, stirring well with a whisk. Add flour mixture to buttermilk mixture, stirring until moist.
Pour batter into prepared baking pan. Bake at 450° for 20 minutes or until a wooden pick inserted in center comes out clean. Cool completely. Cut corn bread into 1-inch cubes.
Reduce oven temperature to 350°.
Bring broth to a boil in a large saucepan; cook until reduced to 5 cups (about 30 minutes). Heat oil in a large nonstick skillet over medium-high heat. Add 1 cup onion; sauté 3 minutes. Add corn and bell pepper; saute 3 minutes.
Combine onion mixture, corn bread, French bread, and green onions in a large bowl, stirring to combine. Add broth, tossing to coat. Spoon mixture into a 13 x 9-inch baking pan coated with cooking spray. Bake at 350° for 40 minutes or until set.