Step 1
Toss pears with lemon juice in a nonreactive bowl.
Step 2
Bring water and sugar to a boil in a 3-quart saucepan over high heat. Boil until reduced by half about 8 minutes. Cool slightly. Pour over pears; stir in brandy. Chill covered 8 hours to overnight.
Step 3
Transfer pears to a small bowl using a slotted spoon. Bring pear liquid to a boil in a saucepan; cook until reduced to about 1/2 cup 7 to 8 minutes. Add pears; return to a boil. Whisk cornstarch and water together. Stir in along with cinnamon. Return to a boil and boil exactly 1 minute. Transfer immediately to a bowl to stop cooking; let cool thoroughly.
Step 4
Set a baking stone baking steel or inverted baking sheet on center rack of oven and preheat to 375 degrees F (190 degrees C). Line 2 baking sheets with parchment paper.
Step 5
Roll out 1 block of pie dough to a roughly 9x13-inch rectangle. Cut out twenty-four 2-inch rounds with a cookie or biscuit cutter or a small glass and cut a small slit in the center of 12. Beat egg with water and kosher salt for the egg wash.
Step 6
Brush edge of each unvented round with egg wash. Add 2 teaspoons filling to the center and top with a vented round. Transfer to the prepared baking sheet and firmly crimp edges with a fork. Brush with egg wash. Chill or freeze while repeating process with remaining dough and filling to make 12 more poppers.
Step 7
Set a baking sheet with poppers on the preheated stone; bake until deeply golden brown 20 to 25 minutes.
Step 8
Whisk together milk and vanilla in a small bowl then whisk in powdered sugar until glaze is smooth and very thick. Transfer to a pastry bag or zip-top plastic bag with a snipped-off corner. Drizzle glaze on each popper. Let glaze set up about 30 minutes before serving.