Make the crust first:

1. Place dry ingredients in food processor and pulse to mix. Add cubed butter and pulse about 12 times until the butter and shortening are mixed throughout. Slowly pour the water/vodka mixture through the lid while pulsing, until the dough begins to clump. Give it one more good, long pulse until you see it starting to form a ball.
2. Transfer the dough to a piece of plastic wrap or parchment and press together to form a flat, round disc and chill for 20-30 minutes.
3. Prepare your filling while it chills and preheat oven to 400 degrees with a pizza stone, baking steel, or large cookie sheet.
4. To prepare filling: place all filling ingredients except butter in a bowl and mix well to combine.
5. After chilling, roll dough out on a floured surface (I like to do it on the parchment I'll bake it on later) until you have about a 12 inch circle, and a thickness of about ¼ inch. The edges don't have to be perfect, just make sure to keep moving the dough and adding flour while rolling to make sure it isn't sticking (you don't have to worry too much about this if you're rolling it on parchment.)
6. Place rolled out dough in refrigerator for 5-10 minutes before adding filling.
7. Place rhubarb and all their "goo" in the center of your rolled out crust, leaving a one inch border.Trim any very uneven edges if desired and fold edges of dough over the filling, folding and crimping as you go. Brush edges and folds with egg wash and sprinkle with a light dusting of granulated sugar, dot the top of the rhubarb filling with butter, and slide into the oven, either on a preheated pizza stone, baking steel, or preheated sheet tray.
8. Bake for 25-30 minutes, until crust is golden brown and filling is bubbly. Let cool for 20 minutes and serve slightly warm with vanilla ice cream or whipped cream.