In medium bowl, whisk together granulated sugar, brown sugar, butter, eggs, vanilla, lemon zest and 1 tablespoon lemon juice until thoroughly combined. Add flour, baking powder and pistachios; stir until combined. Spread mixture into prepared pan.
Bake 32-37 minutes or until lightly browned at edges and center is set. Cool completely in pan on cooling grid. Using parchment paper as handles, lift blondies out of pan and cut into 24 triangles.
In small bowl, whisk together remaining 1 tablespoon lemon juice and confectioners' sugar. If glaze is too thick, add up to 1 teaspoon water. Drizzle blondies with glaze.