Prepare the Dough: In a food processor, sift together the flour, sugar, and salt. Add the cold, cubed butter and pulse until the butter pieces are no larger than the size of peas. Slowly drizzle in the ice water, a few tablespoons at a time, until the dough just starts to hold together. If the dough feels too wet or sticky, dip your hands in flour and gently knead the dough a few times. Divide the dough into two equal portions, cover with plastic wrap, and refrigerate for a couple of hours to chill.
Prepare the Blueberry Filling: In a small bowl, toss the blueberries with lemon juice, lemon zest, and cornstarch. Set aside.
Assemble the Pie Cookies: Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. Dust a work surface with flour and roll out one half of the chilled dough until thin but not fragile. Use a round cutter (about 2.5 inches in diameter) to cut out 20 rounds of dough. Place 10 rounds on the prepared baking sheet and spoon a few blueberries onto each round. Place the remaining 10 dough rounds over the top of the blueberries and press down the edges to seal. If the edges don’t stick, use an egg wash to help seal them. You can use the end of a chopstick dipped in flour to crimp the edges. Once all the pie cookies are sealed, brush the tops with an egg wash for a golden finish.
Bake the Pie Cookies: Bake the pie cookies in the preheated oven for 15-18 minutes, or until they are a beautiful golden brown. Remove from the oven and cool completely on a wire rack.
Assemble the Ice Cream Sandwiches: Once the pie cookies are completely cooled, place a small scoop of vanilla ice cream between two pie cookies and gently press together to form a sandwich. Serve immediately or wrap and store in the freezer until ready to serve.