Mix all the ingredients for the marinade together in a small bowl and rub over the lamb.
Season the lamb liberally with salt and pepper transfer into a lidded container and store in the fridge overnight.
Take the lamb out of the fridge for 30 minutes. Preheat the slow cooker (this will speed your cooking time considerably) while you prepare the lamb.
Heat a large non-stick frying pan and sear the lamb over high heat on all sides until nicely browned. Set aside.
Add the potatoes and onion to the pan and fry, stirring, over high heat until the potatoes are starting to colour a little. Deglaze the pan with splash of the wine. Season with salt and pepper.
Transfer the potatoes to your slow cooker. Add the cinnamon stick, lemon slices and bay leaves.
Top with the seared lamb. Pour the wine, stock and vinegar over the lamb.
Cook on low setting for 7-8 hours, or until the lamb is tender if pierced with a knife and falling off the bone.
If you wish to brown the lamb for some colour (this is optional) place under a hot grill for about 5 minutes. Rest for 10 minutes, loosely covered.
Shred or carve the lamb into portions and serve over the potatoes sprinkled with a little feta cheese, garnished with the fresh herbs and with extra lemon wedges on the side.
Instant Pot method
Follow steps 1-5 and cook in your Instant Pot for 45 minutes at high pressure. Allow around 25-30 minutes of natural release.
If you wish to brown the lamb for some colour place under a hot grill for about 5 minutes. Rest for 10 minutes before slicing to serve.
Follow steps 1-5. Preheat the oven to 160°C (320°F).
Place the potatoes and onion on in a large (turkey) roasting bag and top with the lamb. Add the cinnamon stick, lemon slices and bay leaves. Place on a heavy deep roasting tray.
Add 60ml (1/4 cup) of white wine or stock and seal the bag. Add a small hole to allow some steam to escape.
Cook for 3 1/2 hours. Remove from the oven and very carefully open the roasting bag – the steam can give you a nasty burn so protect your hand!
Return to the oven for another 30 minutes to brown if needed. Check the internal temperature with a digital thermometer. It should be 62°C/ 145°F (medium rare), 71°C/160°F (medium), or 76°C/170 °F (well done). Leave the lamb to rest for 10 minutes loosely covered with foil before slicing to serve.
The cooking juices from the lamb can be transferred to a fat/gravy separator to remove some of the oil. Mix with the shredded lamb or simmer for 30 minutes at low temperature until slightly reduced to use as gravy with the sliced lamb.You can use butterflied leg of lamb instead of lamb shoulder, cut into large pieces if needed.