- Heat oven to 150°C/fan 130°C. Combine the salt, ground cumin, smoked paprika, garlic granules and dried oregano in a small bowl.
- Arrange the rib racks in a single layer on a large chopping board or clean kitchen counter. Season with the dry-rub on both sides, patting it down into all the nooks and crannies.
- Double wrap each rack in foil; seal into a tight parcel. Arrange the rib parcels in a single layer on one (or two) baking sheets and bake until the ribs are very tender but not quite falling apart, around 2 ½ hours.
- Meanwhile, combine the chimichurri ingredients in a bowl; season with sea salt and freshly-ground black pepper, to taste. Cover with cling film and set aside.
- Take the ribs out of the oven. Increase the oven temperature to 230°C/fan 210°C. Line a large baking sheet with foil. Unwrap the rib parcels. Using tongs, carefully transfer the rib racks to the foil-lined baking sheet, leaving the juices behind. Roast for 10 minutes, or until browned.
- Transfer the ribs to a serving platter. Generously slather them with the chimichurri and serve, with extra chimichurri on the side.