1. Melt butter in a large soup pot over medium heat and add onion, carrots, and celery. Cook until vegetables are tender, about 5 to 6 minutes, then stir in garlic and cook for 30 seconds.

2. Sprinkle flour over the vegetables and stir constantly for 1 to 2 minutes until the mixture is thick and the raw flour smell is gone.

3. Slowly pour in chicken broth while whisking to combine with the roux, then add diced potatoes and bring to a gentle simmer. Cook for 10 to 12 minutes until potatoes are fork tender.

4. Stir in cooked chicken, frozen peas, and milk or cream. Add thyme, salt, and pepper, then simmer on low heat for another 10 minutes, stirring occasionally.

5. Taste and adjust seasoning. If the soup is too thick, add more broth or milk. For thicker soup, simmer uncovered a few extra minutes.

6. While the soup simmers, bake or reheat puff pastry or biscuit rounds according to package instructions and cut into small pieces.

7. Ladle soup into bowls, top with pastry pieces if desired, and serve immediately.