SOUP: In 4-quart Dutch oven, melt butter. Add potato, pear and onion; cook covered, over low heat, stirring often, 20 minutes, until potato is tender. Add chicken broth and thyme; bring to a boil. Reduce heat to low, cover; simmer 8 minutes. Add peas and watercress; bring to boil. Reduce heat; simmer 3 minutes. In blender, puree in batches. Add salt and pepper. LEMON-PEPPER CREAM; Whisk together ingredients. To serve: Ladle 1 cup soup into each of 8 bowls. Serve hot, at room temperature or chilled. Drizzle with Lemon-Pepper Cream. Garnish with watercress.