Put the beetroot in a large pan of water, bring to the boil and simmer until tender – check with a skewer; you may need to remove smaller ones first while the larger ones carry on cooking. Drain and cool, then put on rubber gloves to peel the skin and remaining stalks. Chop into large chunks and set aside two-thirds for later.
Put the remaining one-third beetroot in a food processor or blender with the ginger, garlic, chilli, chopped coriander, cardamom pods, tomato paste, treacle, cumin, ground coriander, fennel seeds, cloves and 2 tsp ground black pepper. Whizz to a paste.
Heat oven to 160C/140C fan/gas 3. Heat half the oil in a big flameproof casserole. Fry the beef chunks in batches until browned all over, removing to a dish as you go. Add the remaining oil, lower the heat, then tip in the onions and fry gently until softened, scraping up the beefy bits. Tip in the spice paste and fry for 5 mins until really fragrant. Return the beef and stock cubes with enough boiling water from a kettle to cover. Bring to a simmer, then put on the lid and bake for 2 hrs.
Uncover and bake for a further 30 mins until the beef is really tender. Put back on the hob and stir in the garam masala and reserved beetroot to heat through. Season well with salt, scatter with coriander leaves and serve with naan, basmati rice and raita or yogurt, if you like.
