Combine 1 bunch sliced celery, 1 teaspoon salt, and water to cover in a medium skillet. Bring to a boil; reduce the heat to medium low and cook until most of the liquid is absorbed. Push the celery to one side of the skillet. Add 2 tablespoons each butter and flour and 1/4 teaspoon each nutmeg and pepper to the other side; cook, stirring, 3 minutes. Add 2 cups milk; cook, stirring all of the ingredients together, until creamy. Season with salt and pepper. Mix 1/2 cup breadcrumbs, 3 tablespoons grated parmesan, 3 chopped scallions and 2 tablespoons chopped parsley; sprinkle over the celery mixture and broil until golden.