To the bowl of a food processor, add the flour, cornstarch, baking powder, sugar, salt and cinnamon and pulse a few times to combine.

Add in the cubed butter and continue pulsing a few times until the butter forms pea-sized pieces. Add the water and pulse a few more times, just until incorporated. The dough should stick together when you press it together between two fingers.

Turn the dough out onto a nonstick work surface, and use your hands to shape the dough into a rectangle, wrap in plastic wrap and refrigerate for 30 minutes. While the dough chills in the fridge, preheat your oven to 350˚F / 175˚C and line two sheet pans with parchment paper.

In a bowl, stir together the sugar and cinnamon. In a separate bowl, whisk together the egg white and water.

Remove the dough from the fridge and divide it in half. On a lightly floured surface, roll out half of the dough into a very thin (about ⅛" thick) rectangle.

Brush a very thin layer of egg white on the dough, then sprinkle with a thin layer of cinnamon sugar. Carefully lift the rectangle from the surface and transfer to a prepared baking sheet, placing it cinnamon sugar side down.

Brush the top with a very thin layer of egg white, then sprinkle with an even layer of cinnamon sugar and press it into the dough gently.

Using a small pastry cutter, first cut the dough lengthwise into ¾" thick strips. Then cut perpendicularly to the strips in ¾" increments. You should be left with a sheet pan full of roughly ¾" squares.

Bake for 12 minutes, until the bottoms are golden brown. Let them cool completely on the sheet pan. Repeat with the other half of the dough.