This ingredient is just cider that has been boiled into a thick syrup, resulting in a very concentrated apple flavor. You can buy it or make your own at home.
Pour pure cider into a stock pot much bigger than whatever quantity of cider you're using. There should be plenty of room for it to bubble without boiling over.
Reduce it to ⅓ to 1/7 of its original volume, allowing it to boil for three to eight hours. Stir it periodically so it boils consistently and doesn’t burn in the pot.
Combine all the other ingredients for your pie filling with about ¼ cup of your homemade or store-bought boiled cider before assembling it inside the unbaked crust.
The result is going to be a pie with a super rich, powerful apple flavor with seasonal sweetness and tang in every bite — no bland, slimy filling here.