Using a sharp knife, cut the pumpkin in half and scoop out the seeds.
Using a vegetable peeler, peel away the outer rind.
Cut the halves into one to two-inch slices and then cut each slice into one-inch cubes.
Heat the olive oil in a large soup pot on medium heat.
Add the leeks, onion, minced sage, thyme springs, rosemary sprig, and 1 teaspoon salt and sauté until the leeks and onions are translucent, about 10 minutes.
Add the pumpkin cubes and the chicken broth or bone broth and bring to a boil. Then, immediately reduce the heat to a medium simmer.
Cover the soup pot and allow the soup to simmer until the pumpkin is tender, about 20-30 minutes.
Once the pumpkin is tender, turn off the heat and remove the rosemary sprig and remaining thyme stems. (The leaves from the thyme sprigs should have fallen off, and all that should remain are the thyme stems. If not, allow the thyme to cool and then gently pull off the leaves and add them to the soup.)
Purée the soup using an immersion blender. If you do not have an immersion blender, allow the soup to cool slightly, purée the soup in batches in a blender or food processor, and then return the soup to the soup pot.
Add the butter to the soup and stir the soup as the butter melts.
Pour the cream into the soup and stir.
Add a bit of freshly grated nutmeg, no more than 1/8th of a teaspoon.
Taste the soup and add additional salt if desired.
You may also add a few twists of freshly grated black pepper if desired.
Serve immediately with optional toasted baguette slices.
Store leftovers in an airtight container in the refrigerator. The soup will stay fresh for approximately 4 days. You can also freeze the soup in a freezer-proof container. Your frozen soup is best consumed within 3 months.