I recently made a cake with lots of blueberries, and (with a recently calibrated thermometer, close to sea level) found an internal temperature of 101.0C at one spot, several centimeters away from the edge. (The rest of the cake was at 93-97 C or so.) It turns out that sugar elevates the boiling point of water by a few degrees, so the hot spot may have been a big clump of berries touching the bottom of the pan. If you're using the temperature method on a nonhomogeneous cake, always check multiple spots!

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