In roasting pan, heat pan juices over medium-low heat to a simmer. Stir in leeks; cook and stir 2 to 3 minutes. Stir in wine, scraping up any roasted bits from bottom of pan; let simmer 5 minutes.
Stir in 1 cup of the broth; continue to simmer 2 to 3 minutes. Meanwhile, whisk rice flour blend into remaining broth until smooth. Whisk flour mixture into leek mixture; cooked and stir 2 to 3 minutes longer or until thickened. Stir in herbs, salt and pepper.