Pre-heat oven to 350 degrees. Place pumpkins and sweet potatoes on lightly greased baking sheets. Drizzle with olive oil and season with salt and pepper. Roast in the oven for about 30-35 minutes, or until fork tender. Remove and set aside. Heat 1 Tbs. oil in a large sauce pan over medium heat and add garlic and ginger, let cook 1 minute. Add roasted pumpkin, roasted sweet potato, pumpkin pie spice and dried thyme, toss to coat evenly. Let cook 3-5 minutes then add chicken broth and bring to a boil. Reduce heat to a simmer, cover and let cook 15-20 minutes. Using an immersion blender, begin pureeing the ingredients, or puree in batches using a blender and return to pan. Add milk and heavy cream and stir until completely combined. Heat thoroughly but do not boil at this point. Garnish with dots of white truffle oil.