You certainly can use the flavorful leftover chicken stock to make a delicious chicken gravy. Make a smooth cornstarch slurry using 1 tablespoon of corn starch and 2 tablespoons of water. Whisk this into the broth, turn on the saute mode and cook for 3-4 minutes until the gravy thickens. If you want you can add in some heavy whipping cream for extra body.