Step 1

Position a rack in the middle of the oven and preheat to 400 degrees. Have a large sheet pan nearby.

Step 2

Use a fork to prick the squash skin all over, then lay it on the sheet pan. Roast for 1 hour, or until the skin has softened and a knife inserted in the flesh goes in easily. Let cool slightly.

Step 3

Cut the roasted squash in half lengthwise, through the stem. Scoop out and discard the seeds. Scoop the flesh into a bowl; discard the spent halves.

Step 4

In a 2-quart or larger pot over medium heat, heat the oil until shimmering. Add the onion and garlic and cook until they start to soften, 2 or 3 minutes. Add half of the sage, reserving the rest for garnish, and cook until aromatic, a few minutes. Add the roasted squash and broth. Increase the heat to medium-high and bring to a boil. Reduce the heat to medium-low or just enough so the liquid is gently simmering, cover and cook, stirring once or twice, to bring all the flavors together, about 10 minutes.

Step 5

While the soup is cooking, place the cream in a deep large bowl and use a balloon whisk or hand mixer to beat the cream until it barely forms soft peaks.

Step 6

Remove the soup from the heat. Use an immersion blender to puree the soup until smooth. (Or, you can puree the soup in batches in a blender: To prevent splatters, be careful to not fill it more than halfway, remove the center ring from the lid, and hold a kitchen towel over the lid as you blend.) Season to taste with salt.

Step 7

Divide among individual bowls. Top each portion with a dollop of the whipped cream and some of the remaining chopped sage. Serve hot.