In a food processor, add flour, cornstarch, baking powder, sugar, salt, and cinnamon. Pulse a few times to mix.
Add the chilled cubed butter and pulse until it forms pea-sized pieces. Add ice water and pulse just until the dough comes together.
Turn the dough onto a work surface, shape into a rectangle, wrap in plastic, and chill for 30 minutes. Preheat oven to 350°F and line two baking sheets with parchment paper.
Mix the sugar and cinnamon for the coating in a small bowl. In another bowl, whisk the egg white with water.
Divide the chilled dough in half. On a lightly floured surface, roll one half very thin (about 1/8 inch thick).
Brush a thin layer of egg white mixture on the dough, then sprinkle with cinnamon sugar. Carefully lift and transfer to a baking sheet, placing the cinnamon sugar side down.
Brush the top with more egg white, then sprinkle another even layer of cinnamon sugar. Gently press it in.
Use a pastry cutter or knife to cut the dough lengthwise into 3/4-inch strips, then cut crosswise into 3/4-inch squares.
Bake for 12 minutes until the bottoms are golden brown. Let cool completely on the sheet pan. Repeat with the remaining dough.
Notes
Nutrition per serving: Calories: 237, Total Carbs: 31g, Net Carbs: 30g, Fats: 11.7g, Protein: 2.6g.