Preheat oven to 375 degrees. On a lightly floured work surface, roll puff pastry into an 11 inch square. Using a plate as a guide, cut out a 10 inch circle. Refrigerate until ready to use.
In a medium cast iron skillet, combine sugar, balsamic glaze, and 3 tablespoons of water. Cook over medium heat until it becomes fairly thick and syrupy.
Stir in butter. Place pear slices in the mixture and reduce heat to medium-low. Cook the pears in the mixture about 10-15 minutes.
Remove skillet from heat. Drape the chilled pastry circle over the pears, tucking under the edges. Bake about 20-25 minutes until the pastry is golden brown.