• Preheat oven to 350°F if using a glass pan. See Note if using a metal pan.  Lightly grease a 13×9-inch pan and set aside.

To prepare the crust:

• In a medium bowl whisk together sugar, flour, baking powder, salt and lemon zest. Using a pasty cutter or food processor cut in the cold butter until the mixture resembles coarse sand. Add the beaten egg and mix until the dough starts to hold together but is till crumbly. Press a little more than half the dough into the prepared pan. Set aside.

To prepare the blueberry mixture:

• In a large mixing bowl combine the sugar, cornstarch and lemon juice. Add the blueberries and toss gently with a rubber spatula to combine. Pour the blueberry mixture over the crust and spread evenly. Crumble the remaining dough (with some larger clumps) over the blueberry layer leaving some blueberries exposed and peaking through the crust.
• Bake for 50-55 minutes or until the top is lightly browned. Cool completely then chill for cleaner cuts. Cut into small squares, bars or wedges. Whisk together the icing ingredients and lightly drizzle each bar as desired.