Combine flour, salt, sugar, and cornstarch in a food processor and pulse
Add the butter and pulse just about 5-6 times.
Pour in the ice water and vinegar pulsing 3-4 times.
You want it to just begin to come together, but still remain crumbly.
Dump out onto a piece of plastic wrap and push into a square.
Wrap well and chill a few hours.
Roll out on a floured surface pretty thin.
Brush with melted butter, sprinkle with the cinnamon sugar mix.
Pop into the freezer 20 mins.
Bake at 400 degrees until crispy. (approx 15 mins but keep an eye on it.)
Let cool.