Preheat an oven to 190 degrees C. Line a baking tray with baking paper.
Roll out half of the pastry to 3mm thick. Cut 16 8cm circles from the pastry. Line 16 cups of a mini muffin tray (you may need two trays) with the pastry circles. Refrigerate to chill, about 15 minutes. Meanwhile, roll out the other half of the pastry to 3mm thick then cut out 16 7cm circles. Lay the 16 circles onto the prepared baking tray and refrigerate.
Mix together the sugar, cinnamon, nutmeg, lemon zest and cornflour in a bowl. Stir in the blueberries then toss lightly to coat with the sugar mixture. Whisk the egg in a small separate bowl. Spoon about 1 tablespoon of blueberry mixture into each pastry-lined muffin cup (don't overfill). Place a lollipop stick horizontally into the filled pop so that most of the end sticks out. With a pastry brush, dab a little beaten egg evenly around the edge of the filled pie shells; place a 7cm top pastry circle onto the filled shell and pinch edges together to seal in the filling and close the pastry around the stick. With a toothpick, poke 3 or 4 steam holes into the top. Brush top of each pie pop with beaten egg then sprinkle with sugar.
Bake in the preheated oven until the tops are golden brown, about 20 minutes. Let cool 5 minutes before gently removing from muffin tray cups. To help pops release, run a small knife around the edges and under stick.
Fresh or frozen blueberries or any other berry can be used; if using thawed berries, place in a sieve to drain the liquid before mixing with sugar and seasonings. Adding too much liquid to the pops can cause them to leak or overflow during baking.
As extra insurance to get pie pops to release from muffin cups, cut out small circles of baking paper and place in bottom of each cup before lining with pastry.