I used small red Bartlett pears, peeled and sliced thinly. Instead of coring the pear, I peel it, cut vertically down both sides until I reach the core, and salvage the small sides around the core for something else. The recipe is incredibly simple, you just need to be prepared for the situation I encountered. You may even consider tilting the pan over the sink to drain some of the liquid before inverting it, and also holding it over the sink during inversion. Also, the longer you wait after the tart has baked, the better the syrup will set up.
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