Preheat oven to 375 degrees F. In a large Dutch oven over medium heat, melt butter and saute shallots until tender, about 3 minutes. Add parsnips and pears, tossing to coat; add 1 cup water. Cover pot and place in the oven. Roast, stirring occasionally, 45 minutes, or until tender. Pour mixture into food processor and process until smooth, adding cream, nutmeg, salt, pepper, and sherry or liqueur.