Preheat the oven to 350F and spray a 9x13 dish with nonstick cooking spray.
Roll out the crescent roll dough. I separated mine into 2 pieces (of 4 crescent rolls). Pinch together any open seams, then lay out both pieces into the baking dish and cover the bottom of the pan. Come up the sides a bit with the dough if you can.
Bake the dough in the oven for approx 12-15 minutes. Make sure to check it as it gets closer to the 12 minute mark so that it does not brown too much.
Meanwhile, make the lemon filling by whisking together the eggs and egg whites, and lemon juice.
Slowly whisk in the all purpose flour and icing sugar, followed by the lemon zest. Mix until it's all well blended.
As soon as you remove the crescent crust from the oven, pour the lemon filling into it, then return it to the oven for 20 minutes or until the filling is set.
Let the squares cool completely before cutting them into 20 squares- 5 down, 4 across.
When you are ready to serve them, dust them with a little icing sugar. Enjoy!