What is the purpose of the vodka? Can I substitute with something else?

Thanks so much. Great concept. I don't suppose it matters that the vodka I have is an open bottle from decades ago. I read online that so long as there isn't an odd odor or color to it, it will only be less potent.

The vodka contributes to a crisp, crunchy coating. (Read more about it here: https://food52.com/blog/8953-cook-s-illustrated-s-foolproof-pie-crust) Vodka is a quite neutral spirit, though you could try bourbon or gin (though they may leave more of an aftertaste!).