In a small saucepan, combine 3/4 cup of the blueberries, the sugar and cornstarch. Stir in 1/4 cup water. Cook over medium heat for 5 to 7 minutes or until berries have popped and mixture has thickened. Remove from heat and stir in remaining 1/4 cup blueberries. Cover and refrigerate for 20 minutes.
Heat oven to 425 degrees . Unroll one of the piecrusts on a cutting board. Cut out circles with a 2 1/2-inch cookie cutter. Gather together scraps, re-roll and cut out circles (you should have 16 total). Repeat with second piecrust.
Divide 16 of the rounds between 2 cookie sheets. Gently press a pop stick into each round. Spoon a heaping teaspoon of the blueberry filling in center of each round. Brush edges with egg mixture and place a second round on top. Seal edges with a fork, brush tops with egg wash and sprinkle pies with a little sugar. Cut small vent holes into each pie.
Bake at 425 degrees for 10 to 11 minutes. Remove with a thin spatula to a wire rack. Cool slightly and serve.