Melt the butter in a Dutch oven over medium-high heat. Add leek and celery; sauté 2 minutes. Sprinkle with flour, stirring to coat. Add potato and next 5 ingredients (potato through broth). Bring to a simmer over medium heat. Reduce heat to low. Cover and cook 6 minutes or until thoroughly heated. Add scallops, and cook 2 minutes or until scallops are done. Stir in half-and-half and parsley.