Two days before you are planning to barbecue, mix the rub together and put into a large ziplock bag. Add the beef ribs and massage the barbecue rub into the flesh.
Meanwhile, up to 2 days in advance make the glaze. Heat the oil in a large pan and sauté the onions and chilli for about 10 minutes until softened. Add the maple syrup, sugar and cider and bring to a simmer, stirring to combine. Remove from the heat and whisk in the mustard, Worcestershire sauce and tomato puree. Blitz with a hand blender until smooth. Set aside to cool completely.
Once the ribs have been marinating for two days, preheat the oven to 130°C/275°F/Gas Mark 1. Wash off the rub under cold running water and place in a large heatproof casserole with a lid. Pour over the glaze, cover tightly and roast for about 5 hours or until the beef is very tender. Leave to cool at room temperature and then place in the fridge to chill overnight.
On the day of the barbecue, remove the ribs from the fridge and take off any solidified fat off the ribs. Allow to come back to room temperature and transfer the ribs into a dish ready for the barbecue. Reduce the rest of the glaze down until it will nicely coat the ribs.
If using a charcoal barbecue, light it 30 minutes before you want to start cooking. If using a gas barbecue, light it 10 minutes beforehand. Place the ribs on the barbecue on medium hot coals and cook for 10-15 minutes on each side or until the meat is completely warmed through and the edges are sizzling, basting every 5 minutes or so with the reduced down glaze.
Garnish with the thyme sprigs and serve with a fresh tomato & basil salad (and plenty of napkins!)