Can I boil a yogurt marinade if I add cornstarch?
Good news! There is no reason to bring the marinade to a rolling boil as a simmer will siffice. Chicken and other items that have been in contact with raw chicken are considered safe at 165 degrees (See http://www.foodsafety.gov/keep/charts/mintemp.html). A simmer is generally about 180. If the sauce breaks however, you are correct that a cornstarch slurry should pull the marinade back together no problem. Happy cooking!