Preheat oven to 425°. Place a roasting pan in the oven and preheat for about 10 minutes.
Combine the diced vegetables in a bowl.
Toss well with olive oil.
Transfer oiled vegetables to heated roasting pan.
Place the pan in the oven and roast the vegetables without stirring for 10 min.
Stir the vegetables and roast until tender (stirring every 10 min.) approximately 30 min.
At this point, you may transfer the vegetables to a large bowl and mash or rice them.
Add the whipping cream and butter and mix well.
Season with salt and pepper. sprinkle with toasted pecans.
NOTE: This may be made ahead of time and stored in the refrigerator. To reheat before serving, warm it up to room temperature and bake covered with aluminum foil, in a preheated 350° oven, for 20-25 min. Sprinkle with toasted pecans before serving.