Prepare the Chestnuts
If using fresh chestnuts: Preheat oven to 425°F (220°C). Score an “X” on each chestnut, roast on a baking sheet for 20–25 minutes, then peel while still warm.
If using pre-cooked or vacuum-packed chestnuts, skip this step.
Sauté the Aromatics
In a large pot, melt butter over medium heat.
Add onion, carrot, and celery; cook for 5–7 minutes, stirring, until softened and fragrant.
Stir in garlic and cook for 1 minute more, just until aromatic.
Simmer the Soup
Add roasted chestnuts, thyme, bay leaf, and stock to the pot.
Bring to a boil, then reduce to a simmer.
Cook uncovered for 20–25 minutes, until vegetables and chestnuts are very tender.
Blend Until Smooth
Remove thyme sprigs and bay leaf.
Use an immersion blender to puree the soup until silky. (Or carefully transfer in batches to a blender.)
Stir in cream, then season with salt and pepper to taste.
Finish & Serve
Ladle soup into bowls, drizzle with extra cream, and garnish with fresh parsley or chives.
Cue: The soup should be smooth, pale golden-beige, with a rich nutty aroma and velvety mouthfeel.