Step 1

Heat the butter in a large Dutch oven over medium heat until melted. Add the celery, onion, carrots, garlic and thyme, then add the salt and pepper. Cook until the celery is tender, 4 to 6 minutes. Deglaze with the white wine, scraping the pot with the spatula. Add the vegetable stock and bring to a boil, then reduce to simmer. Let simmer to allow the carrots to soften, about 10 minutes. Stir in the heavy cream and remove from the heat. In 2 batches, transfer the soup to a heatproof blender and blend until very smooth. Return the soup to the Dutch oven and return the soup to a simmer.

Step 2

To serve, ladle into soup bowls. Top each serving with a dollop of sour cream and some of the reserved celery leaves. Crack over black pepper to taste.