Preheat oven to 375 degrees F. Place tomatoes in a small bowl. Pour enough boiling water over the tomatoes to cover. Let stand for 10 minutes to soften. Drain tomatoes; set aside. In a large skillet, melt butter; add onion and cook until tender. Stir in rice, tomatoes, parsley, basil, salt, and pepper. Whisk together the broth and egg. Stir into rice mixture and place in a 2-quart baking dish. Sprinkle with walnuts. Bake, uncovered, for 30 minutes or until set.