Bring first 7 ingredients to a boil in a saucepan over medium heat, stirring until sugar melts. Reduce heat to low; cook, stirring occasionally, 10 minutes.
Spoon half of blueberry mixture into a lightly greased 8-inch square pan. Roll 1 piecrust to 1/8-inch thickness on a lightly floured surface; cut into an 8-inch square. Place over blueberry mixture; sprinkle with pecans.
Bake at 475° for 10 minutes. Spoon remaining blueberry mixture over baked crust.
Roll remaining piecrust to 1/8-inch thickness; cut into 1-inch strips. Arrange in lattice design over blueberry mixture.
Bake at 475° for 10 minutes or until golden. Serve with vanilla ice cream, and garnish, if desired.