Combine all ingredients in a saucepan over medium heat. Bring to a simmer. Lower heat and continue to cook (stirring often) until a syrup begins to form and the mixture is about half the size. 

Set aside and let cool. 

In a bowl, combine butter, flour, and salt. With a pastry fork or your fingers, mix in butter until fulling incorporated. The mixture will have a sandy texture.

Add ice water a little at a time, mixing as you do. Continue to add water until a dough form. Gather into a ball and divide in half. 

Preheat oven to 375 degrees. 

Place half the dough on a floured surface. roll out until about 1/4 inch thick. On a floured piece of parchment paper, repeat with the other half of the dough. 

Using a knife or pizza cutter, remove uneven edges from the dough to form a square/rectangle. 

Scoop about 1 tbsp of filling onto the dough. Spread out slightly (so it's less like a mound) and leave about two inches between each scoop.

Pick up parchment paper holding the top half of the dough. Lay on top of the other half of the dough and press gently to secure around each mound of filling. 

Use a knife or pizza cutter to divide the pop-tarts. Use a fork to press down the sides of each one and poke holes in the top for ventilation. Use a spatula to transfer to a baking sheet lined with parchment paper. 

Repeat until all the dough or filling has been used up. Bake for 25 minutes or until slightly golden (you may have to bake two batches, depending on the size of your baking sheet). Cool completely on a cooling rack. 

Whisk together all icing ingredients until smooth. Add more powdered sugar if too runny and more apple cider if too thick. Use a pastry brush to paint on each pop-tart. Feel free to brush each one more than once!