In a large saucepan, cook the carrot, celery, leek and garlic in the butter over medium heat for about 5 minutes or until tender. Season with salt and pepper. Add the flour and cook for 1 minute while stirring. Add the broth and bring to a boil while stirring. Cover and simmer gently for about 5 minutes. Add the chicken, peas and cheese. Blend well and adjust the seasoning. Allow to cool.