In a small bowl, combine 2 teaspoons kosher salt, ½ teaspoon pepper, 1 teaspoon garlic powder, 1 teaspoon onion powder, ½ teaspoon ground coriander, and ½ teaspoon dried thyme leaves Set aside.
Combine ¼ cup Dijon mustard and 12 ounces apple cider in a small glass measuring cup and set aside.
Pat a pork loin roast dry with paper towels. Using a sharp knife, cut 6-8 slits along the top of the roast, about 1½ inches deep and spaced 3-4 inches apart. Tuck a a couple apple slices into each slit. Rub the prepared spice rub mixture evenly over the pork roast.
Place the seasoned pork loin into the base of the slow cooker. Scatter the quartered onion and any remaining apple slices evenly around the pork. Then pour the apple cider mixture into the slow cooker.
Cover and cook on low for 8-10 hours or high for 4-6 hours, or until the pork is fully cooked through and tender.
To serve, remove the pork from the slow cooker and let rest on a cutting board or platter for 10 minutes. Strain the cooking liquid to remove the onions and apples. Cut or shred the pork loin and serve with the strained braising liquid.
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Notes
Apple Cider: Feel free to substitute the apple cider for hard apple cider, 100% apple juice, or low-sodium chicken stock. Do NOT use apple cider vinegar.Pork Roast: A pork tenderloin can be substituted for a pork loin roast, but should only be cooked for 4 hours on low. Do not cook on high!Apples: Use a firm apples suitable for baking, such as gala, Honeycrisp, or golden delicious. Coriander: Skip if you don't have it or replace with a ⅛ teaspoon cumin for similar warming notes. Leftovers: Store leftover pork roast, with leftover cooking liquid in a sealed container in the fridge for up to 3 days. Alternatively, freeze any leftover cooked pork roast with the cooking liquid in a sealed freezer-safe container (leaving a bit of room for the liquid to expand) for up to 3 months.