2 and 1/2 cups all-purpose flour
1 teaspoon sugar
1/2 teaspoon salt
1 cup (2 sticks) cold unsalted butter, cut into pieces
1/4 cup ice water
8 ounces cream cheese, room temperature
3/4 cup granulated sugar
2 teaspoons lemon zest, plus 1 tablespoon lemon juice
1 large egg
10 ounces frozen blueberries
2 tablespoons all-purpose flour
2 tablespoons heavy cream
1 tablespoon sanding sugar
Pie dough: In a food processor, pulse flour, sugar, and salt. Add butter and pulse until mixture resembles coarse meal, with a few pea-size pieces of butter remaining. Add ice water, pulsing until dough is crumbly but holds together when squeezed (if necessary add up to 2 tablespoons water). Divide dough into 2 disk, wrap each in plastic, and refrigerate at least 1 hour.
Pies: Preheat oven to 400 degrees. Stir together cream cheese, 1/2 cup granulated sugar, lemon zest, and egg until smooth. Toss blueberries with 1/4 cup granulated sugar, lemon juice, and flour.
On a lightly floured surface, roll dough out to 1/8-inch thick circle. Lay 1 dough round on a parchment-lined baking sheet and cut into quarters. Spoon 1 heaping tablespoon cream cheese mixture into center of each quarter. Spoon 2 tablespoons blueberry mixture on top. Brush edges with cream and bring opposite corners together to form triangles; trim if needed. Crimp edges to seal, brush tops with cream, and sprinkle with sanding sugar. Repeat with remaining dough round and fillings. Cut a small vent in each pie and bake until golden, 20 to 25 minutes. Let cool completely on wire racks before serving.