Peel, seed and cut the butternut squash into cubes. Roast in a preheated 375°F oven for 45 minutes. In a large pot or dutch oven, saute the carrot, celery and onion. Add the butternut squash and the chicken stock. Add salt and pepper. Cook for about 15 minutes. Add the pumpkin puree and stir. Puree the soup either with an emersion blender, or in a stand up blender. Once pureed add the half and half. Check for seasoning. Serve with a dollop of mascarpone cheese and croutons. Bon Appetit.