1. Position the oven racks so that they are evenly spaced. Preheat the oven to convection bake at 425°F. Cover two baking sheets with foil and coat lightly with nonstick spray.

2. Cut the squash in half lengthwise and remove the seeds. Place cut side down on one of the baking sheets. Combine the onion and garlic and toss with the olive oil until well coated. Spread them on the second baking sheet.

3. Place the squash on the upper rack in the oven and the onion and garlic on the rack beneath. Roast the onion and garlic for 15 to 20 minutes, until tender, and remove from the oven. Roast the squash for 25 to 30 minutes, until tender. Let cool slightly.

4. Put the onion and garlic into a food processor fitted with the steel blade or a blender. Scoop the flesh from the squash and add to the onion and garlic; process until pureed.

5. Pour the puree into a saucepan and mix in the chicken broth, cream, salt, cayenne, bay leaf, and lemon juice to taste. Simmer for 20 minutes; remove the bay leaf.

6. Serve the soup hot or chilled with a dollop of unsweetened whipped cream.