Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat the oil in a large frying pan, add the beef a few pieces at a time until all the pieces are in the pan, then add the onion and fry over a medium heat, stirring, until the meat is evenly browned.
Stir in the garlic and flour. Gradually mix in the ginger beer, then stir in the tamarind paste, dried chillies and spice, sugar and a little salt and pepper and bring to the boil, stirring.
Transfer to the slow cooker pot and press the beef below the surface of the liquid. Cover with the lid and cook on low for 8–10 hours or until the meat is cooked through and tender.
Stir the beef, then ladle into bowls and top with garlic and coriander croutes (see below) and serve with steamed broccoli.