Heat the oven to 160C/320F. Pat the lamb dry and season all over with the salt and pepper.
Heat 2 tbsp of the olive oil in a 30 cm / 12-inch oven-safe braiser or dutch oven over medium-high heat. Sear the lamb in two batches, 3 to 4 minutes per side, until deep brown on all sides. Set the lamb aside on a plate.
Add the remaining 1 tbsp olive oil to the pot. Add the onions and cook for 5 to 6 minutes, until soft. Stir in the garlic, cumin, cinnamon stick, and oregano and cook for 1 minute, until fragrant.
Stir in the tomato paste and cook for 1 minute. Pour in the white wine and scrape up any browned bits from the bottom of the pot. Let it bubble for 2 minutes.
Add the crushed tomatoes, stock, and bay leaves. Return the lamb and any juices to the pot and bring everything to a simmer.
Cover the pot and transfer it to the oven. Bake for 90 minutes.
Remove the pot, nestle the potatoes into the sauce around the lamb, and season them lightly with salt. Cover and bake for another 45 minutes, until the lamb pulls apart easily with a fork and reaches an internal temperature of about 95C/203F.
Uncover, raise the oven to 200C/400F, and bake for 20 to 25 minutes more, until the potatoes are golden at the edges and the sauce has thickened.
Rest the tava for 10 minutes. Remove the cinnamon stick and bay leaves, scatter parsley over the top, and serve straight from the pot.