In a food processor, mix together flour, sugar, and salt. Pulse in the butter, pulsing until the texture resembles a corse meal.
Pour in ice water (or vodka if using), then pulse everything together until just combined. If dough is too dry and not coming together, add in another tablespoon of water.
Form dough into 2 equal sized disks and wrap each with plastic wrap. Place in fridge for at least 1 hour, but up to 2 days.
to assemble the pop tarts
Remove one of the doughs from the fridge. Generously flour a clean work surface. Working quickly, roll the dough out into a 10″x13″ rectangle.
Using a ruler and a long knife, cut your dough into a perfect 9″x12″ rectangle. Then, cut your rectangle into 9 equal pieces, each 3″x4″.
Use a spatula to transfer the rectangles to a large, parchment-lined baking sheet, leaving at least 1 inch between each rectangle. Once all 9 rectangles are moved onto the baking sheet, place the sheet in the freezer while you repeat the rolling & cutting process with the second half of the dough.
Once all of your dough is cut, preheat your oven to 350°F.
Remove the baking sheet from the freezer. Brush the edges of each of your 9 pop tart bases with an egg wash (this will help the dough to stick together).
Spoon a tablespoon of peanut butter into the center of each pop tart base. Spread it slightly, but not too close to the edges.
Place the remaining dough over the filling of the pop tart. Press down on the edges slightly to seal the dough together. Then, using a fork, create indentations around the entire pop tart.
Brush the remaining egg wash over the pop tarts, then use your fork to create an air hole on the top. Bake for 30 minutes, then allow to cool completely.
for the marshmallow icing
While the pop tarts cool, make the marshmallow icing. Make a double boiler by filling a large sauce pan with a few inches of water. Place the egg whites and sugar in a heat safe bowl and whisk vigorously over the double boiler until frothy and the sugar has dissolved.
Transfer the egg and sugar mixture to a stand mixer fit with the whisk attachment. Add the cream of tartar, salt and vanilla.
Whisk until medium stiff peaks form and the mixture is glossy.
Use an offset spatula to spread a large spoonful of marshmallow fluff over the top of each pop tart. If desired, use a blow torch to toast the tops of your pop tarts! Enjoy!