Preheat oven to 350 and prepare your pan: Line a 9x9 pan with two pieces of aluminum foil, set crosswise with a couple inches hanging over each side; press foil to fit, and lightly grease.
Make the crust: Using a hand mixer, beat Olive Oil and powdered sugar together until well blended, 2 minutes. Beat in 1 cup of flour until no traces appear, reserving the 3 Tbs for the filling. Batter will be crumbly. Press the mixture evenly into the prepared pan and bake for 10 minutes.
While crust is baking, make the filling: Using a hand mixer, beat eggs and sugar together for about a minute, then beat in Balsamic Vinegar. Complete filling by beating in salt, baking powder, and remaining flour.
Once the crust has been in the oven for 10 minutes, pour filling over the top and tilt pan as necessary to fully cover the crust. Return the pan to the oven and bake until golden brown and puffy, 12-13 minutes. Let cool in the pan for 20-30 minutes, then use foil handles to carefully remove the bars from the pan and transfer to the refrigerator. Allow to cool completely -- at least an hour, but preferably longer -- before cutting into 16 bars and serving, dusting with more powdered sugar if desired. Serve cold.
* Alfoos Mango is delightful here, but several other flavors also performed well in test batches. Try Sicilian Lemon, Key Lime, or your personal favorite White Balsamic! The crust also works well with Butter, Blood Orange, or Lemon Olive Oils.
How'd the recipe turn out? Let us know on Facebook or Instagram! #howdoyouharvest