Put the oil, vegetables and tomato purée into the bowl of your slow cooker. Dry the beef pieces with kitchen paper and dust with the plain flour (tapping off excess). Add to the slow cooker together with the wine, stock, rosemary and some seasoning. Stir to combine. Cover and cook on high for 5hr or until the beef is tender. After 5hrs of cooking, make the dumplings. Sift the flour into a large bowl and stir in the suet, parsley and lots of seasoning. Add 100ml cold water and stir to make a soft (and slightly sticky) dough. Remove the lid and discard the rosemary sprigs. Pinch off walnut-sized pieces of dough, gently roll into a ball and place on top of the stew, spacing apart. Recover and cook for 1hr more. Check the seasoning and serve with mashed potatoes.