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Add cup (113 g) of unsalted butter to a large stock pot. Heat it on medium until the butter melts completely, which should take about 3 minutes. When the butter is melted, add 1 chopped medium onion, 2 stalks of chopped celery, and 3 medium carrots that have been peeled and chopped to the pot. Cover it, and allow the veggies to cook until they're tender, which should take about 12 minutes. Stir the vegetables occasionally as they're heating to ensure that they cook evenly. When the vegetables are tender, add cup (64 g) plus 1 tablespoon (8 g) of flour to the pot. Stir well with a wooden spoon to mix it in, and allow the mixture to cook for another 2 minutes. Add 7 cups (1.6 l) of chicken broth to the pot. Allow the mixture to come to a boil, stirring it constantly. It should take approximately 5 to 7 minutes to reach a boil. You can use homemade or store-bought broth. If you use store-bought, opt for a low-sodium variety. You'll need 3 sprigs of parsley, 3 sprigs of fresh thyme, and a bay leaf to flavor the soup. Create a bundle with them, and use a piece of kitchen twine to secure them together before adding them to the pot. After you've added the herbs, reduce the heat to medium-low. Cover the mixture, and allow it to simmer, stirring it occasionally. When the mixture has finished simmering, mix in 2 cup (385 g) of cooked, diced chicken. Raise the heat to medium-high again, and return the mixture to a boil, which should take about 5 minutes. You can shred the chicken if you prefer. Once the mixture comes to a boil again, take the pot off the heat. Add cup (118 g) of heavy cream, 2 teaspoons (10 ml) of dry sherry, 1 tablespoon (18 g) of kosher salt, and some freshly ground black pepper to taste to the pot. Stir well with a wooden spoon to ensure that all of the ingredients are combined. Use a spoon to lift the bundle of parsley, thyme, and the bay leaf out of the soup and discard it. Ladle the soup into 4 to 6 bowls. Use 2 tablespoons (2 g) of chopped flat-leaf parsley to garnish the bowls of soup. Serve the soup immediately while it's still hot.

Summary:
Melt the butter. Cook the vegetables in the butter until they're soft. Mix in the flour and cook for another couple of minutes. Stir in the broth and bring the mixture to a boil. Tie the herbs together with kitchen twine and add them to the pot. Simmer the mixture for 15 minutes. Add the chicken and bring the mixture to a boil again. Mix in the cream, sherry, salt, and pepper with the pot off the heat. Remove the herb bundle and spoon the soup into bowls. Garnish the bowls with parsley and enjoy.