Halve and core pears. Set aside one pear half. Quarter remaining pears and transfer to a large bowl. Squeeze lemon over pears and set aside.
Combine sugar and 3 tablespoons water in an 8-inch cast-iron skillet. Bring mixture to a boil over medium-high heat; immediately reduce heat to medium and cook until mixture begins to thicken and turn amber. Remove from heat and stir in butter.
Place reserved pear half in center of skillet along with any reserved juices. Decoratively arrange remaining pears, cut side up, in an even layer. If fruit does not completely fill pan, tart will collapse when inverted.
Place skillet over low heat and cook until syrup thickens and is reduced by half, about 20 minutes. Do not let syrup burn. Remove from heat and let cool.
Preheat oven to 375 degrees.
Roll out pate brisee to a 10-inch circle, about 1/8-inch thick; transfer to a baking sheet and chill until firm, about 30 minutes.
Place pÃ¢te brisÃ©e over pears and tuck in edges. Transfer skillet to oven and bake until golden brown, about 40 minutes. Transfer to a wire rack and let cool 15 minutes. Loosen pastry from skillet using a sharp knife. Place a rimmed platter over skillet; quickly and carefully invert. Serve immediately.