Place the pumpkin cut side up on a parchment lined baking sheet. Season with 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper. Invert to the cut side down, and drizzle with 1 tablespoon of the olive oil. Place in the oven and roast until the skin is golden brown and the pumpkin is tender, 50 to 60 minutes. Remove from the oven and allow to cool. Once cool enough to handle, use a spoon to scoop the pumpkin flesh from its skin and set pumpkin aside until ready to use. Discard the skin.
Set a medium saucepan over medium-high heat. Add the remaining 2 tablespoons of olive oil and, when hot, add the cinnamon and allspice and cook, stirring constantly, for 1 minute. Add the onions, carrots, celery, ginger and garlic to the pan and saute, stirring occasionally, until lightly caramelized, 3 to 4 minutes. Add the chicken stock and reserved pumpkin to the pan and bring the stock to a boil. Reduce to a simmer and cook the soup for 15 to 20 minutes, or until the vegetables are soft.
Remove the soup from the heat and process with an immersion blender (*or in batches in a blender) until smooth. Season with the remaining 1/2 teaspoon salt and pinch of pepper. Add the cream to the soup and stir to combine.
To serve, place 1 cup of the soup in each of 6 warmed soup bowls. Drizzle 2 teaspoons of the pumpkin seed oil in the bowl and garnish with a 2 or 3 fried sage leaves.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.