Preheat oven to 400 degrees. Cut squash in half lengthwise; scrape out seeds. Place cut side down on a cookie sheet. Pour very hot tap water around squash to a depth of 1/4 inch. Bake until tender, approximately 40 minutes, additional water as needed. Remove from oven; let cool to room temperature. Remove squash from shells and reserve. In medium saucepan, cook leeks and onion in butter until tender. Add squash, broth, and thyme. Simmer 30 minutes. Puree in food processor or blender (in batches if necessary). Return to pan and add cream. Season to taste with salt and pepper.
Garnish with dollop of sour cream, chives, and crisp bacon