When testing doneness in most cooked foods, the coldest part will be the very center of the thickest portion. With larger foods, you can take quick readings with your thermometer in several locations to verify that the entire portion is done. If you are chilling food, the center of the thickest part will be the last to cool. Most digital thermometers have small sensors at the probe’s tip. Penetrate the food you are checking with the probe and place the very tip of the probe where you want to measure.