Place the chopped apples, cranberries, apple cider and brown sugar in a saucepan over medium heat.
Cook for about 20 minutes, stirring constantly until you reach a uniform, sauce-like consistency.
Squish all of the cranberries or apple bits with a spatula or masher - they should give easily.
Take off of the heat - it will thicken as you prepare the tart shells.
Poke your thawed tart shells with a fork to prevent the pastry from expanding drastically in the oven.
Bake according to package directions.
Fill the tart shells with 2 Tablespoons of the apple-cranberry sauce.
Melt the white chocolate chips in a microwave-safe bowl along with the shortening, heating for 25 seconds, then stirring, and repeating as needed.
Using a spoon (or a piping bag if you're fancy), drizzle the white chocolate over the tarts - leave a couple plain for those who don't want the drizzle.
Serve warm or cold - either way they are delicious!