Preheat oven to 375.
Slice the squash lengthwise and scoop out seeds and pulp. Place the two squash halves flesh side down on a greased baking pan. Roast about one hour, until the squash can be easily pierced with a knife. Set aside to cool.
Place the onions, garlic, olive oil and 1 cup water in a saucepan and bring to a boil. Reduce to a simmer and cook, stirring occasionally, until the water evaporates. Continue cooking and stirring on low until the onions are translucent.
Scrape the flesh from the squash with a large metal spoon. Add squash, chicken stock and Verjus to the onions. Bring to a boil and simmer 20 minutes.
Puree in batches in a blender or food processor and pass through a sieve.
Add the heavy cream and season to taste with salt and white pepper.
Garnish with pepitas, if desired.
* Note: If using canned chicken stock, reduce 4 cups unsalted to 2 cups.