Heat the oil or butter in a large pan over medium-high heat.
Toss the pork in flour, season with salt and pepper, and brown it in batches until golden. Set aside.
In the same pan, cook the onion and carrots until softened, then stir in the garlic.
Pour in the cider, scraping up any browned bits. Stir in the mustard, then return the pork to the pan along with the apples, thyme, and stock.
Bring to a simmer, cover, and cook gently for 1½–2 hours, stirring occasionally, until the pork is tender and the sauce thickened.
Stir in the cream if using, and season to taste before serving.
Notes
To Cook in the Slow Cooker: Brown the pork first if possible, then transfer everything to the slow cooker. Use 400ml cider and 350–400ml stock (less liquid than the hob version). Cook on LOW for 7–9 hours or HIGH for 4–5 hours. Add the apples in the last hour if you want them firmer, and thicken the sauce with a cornflour slurry near the end. Stir in cream before serving if desired.