Put the whole-wheat pastry flour, all-purpose flour, sugar, and salt into a food processor fitted with a metal blade. Pulse once or twice to blend. Add the cubes of butter and pulse several times until the butter is the size of little peas and blended into the flour. Add the ice water and pulse just a few times more to form a moist, crumbly dough. If you don't have a food processor, you can make this dough by hand in a large bowl using a pastry cutter.

Turn the dough out onto a floured board and press together into a disc. If it seems too dry to hold together, dribble on a little more cold water, a teaspoon at a time, until it forms a dough. Wrap in plastic and refrigerate for at least 30 minutes.

While the dough is chilling, make the filling. In a small saucepan, stir the cornstarch into the lemon juice until it dissolves. Add the blueberries, sugar, and lemon zest. Set over medium heat and cook, stirring regularly, until the sugar dissolves and the blueberries begin to release their juices and color the pan (2 to 3 minutes). Remove from heat.

After 30 minutes of chilling, use a rolling pin to roll the dough onto a floured board until it is about 9 x 15 inches. Cut it crosswise into 5 rectangles of dough (each will be 3 by 9 inches). Spoon the blueberries onto one end of each rectangle of dough, being sure the blueberries don't get too close to the edges (leave at least a half inch of room). Fold the non-blueberry end of the dough up and over the blueberries until the edges meet. Use the tines of a fork to gently press the sides of dough together to form a tight seal. Don't worry if a little of the blueberry juice travels out.

Once all 5 pies are formed, use a spatula to transfer them onto the baking sheet and refrigerate another 30 minutes.

Eat while still warm or at room temperature. Will keep for up to 3 days.