To prepare the filling

1. Melt butter in a medium saucepan.
2. Combine all other ingredients and add to the pan with the butter. Stir frequently over medium heat until cranberries have burst and filling is thick and somewhat uniform, about 15 minutes. Allow to cool in the refrigerator for several hours or overnight.

To prepare the pastry

1. Combine flour, salt and sugar in a medium sized bowl.
2. Cut in butter and shortening with a pastry cutter or fork until it is the consistency of a course meal with small, pea-sized chunks of butter throughout. Add water one tablespoon at a time, tossing gently until pastry comes together in moist clumps. Divide dough in half and pat into two round, flat disks. Wrap with Saran wrap and refrigerate for at least an hour.

To assemble

1. Roll out one disk of pastry on to a floured surface to 1/4″ thickness. Using a 3″ biscuit cutter, gently cut rounds of dough. Each Pop-Tart will require two rounds (one for top and one for bottom).
2. Place one tablespoon of cooled filling on top of half of the rounds.
3. Top the filled rounds with a second circle of of crust and use a fork to crimp the edges. Vent the top of each rectangle by poking the top of the pastry with a fork 2-3 times. Freeze the pop tarts on the baking sheet for at least 2 hours or up to a week.
4. When ready to bake, preheat the oven to 375 degrees. Bake the tarts, uncovered, for 25-30 minutes or until golden brown. Allow to cool and top with sifted powdered sugar or a glaze of choice.