– Melt the butter in a heavy pot over medium-low heat. Add the celery, onion, and garlic. Cook until the onion looks transparent, about 4 minutes.
– Stir in the flour and cook for 1 minute. Pour in the broth and stir in the pecans, then bring to a boil over high heat. Cook until the vegetables are tender and the celery is cooked (about 10 more minutes).
– Turn the heat off and allow to cool for a few minutes. Working in batches, process the pecans, broth, onion, and celery mixture in your blender until you have a smooth texture (about 1 to 2 minutes). Return the soup to the pot, using a strainer if necessary. Stir in the heavy cream and bring the soup to a simmer (uncovered) over medium heat. Season the soup with salt and pepper to taste. Drizzle with olive oil if desired.