Sear the pork: Heat a pan over high heat and sear the pork for a few minutes until browned all over. Transfer to the slow cooker.
Add vegetables & seasonings: Add the onions, carrots, and celery, along with the dried herbs and mustard. Pour in the cider and chicken stock, season with salt and pepper, and stir well.
Slow cook: Cook on high for 2 hours or low for 5 hours until the pork is tender.
Add peas & fresh sage: Stir in the peas and chopped fresh sage, then cook for another hour.
Serve: Spoon over buttery mashed potatoes with crusty bread to soak up the rich cider gravy.
