Preheat the oven to 150°C, fan 130°C, gas 4.
Peel the carrots and cut diagonally into big chunks.
Heat half the oil and the butter in a heavy-based ovenproof dish and fry the steak in batches until browned. Transfer to a plate as you go.
Meanwhile, peel the onion and slice finely.
When all the steak is browned, heat the remaining oil in the same pan and gently cook the onions for about 10 minutes until soft.
Sprinkle on the flour and cook for 1 min, stirring, then return the steak to the pan, add the carrots, stock (or water) and thyme. Cook in the oven for 2½ hours – you will need to give it a stir every so often and add a little more a stock (or water) if necessary. Cover the pan with a lid. Add the redcurrant jelly and cook for another 15-30 mins or so until the meat is really tender.
Serve with the mashed potato and some steamed cabbage, if you like.