There are lots of winter leaves out there apart from our native cabbages and greens. Swiss chard is a great leaf, although it's often quite off-putting for the size of its stalks which shouldn't be thrown away, but just chopped and cooked separately from the leaves. It also comes in different colours and is sometimes sold as rainbow chard. Black cabbage or cavolo nero is another great winter leaf, but takes a fair bit of cooking.
For this dish, you can grill your fillet as individual steaks or cook it as a piece then cut it into steaks so you have the nice rare slice showing. Also, I prefer not trimming all of the chain and skin off as they have so much flavour. For the sauce, I've used some elderberries that I always freeze when they are in abundance in the autumn – but even easier are the suggestions below.
600-700g beef fillet
Salt and freshly ground black pepper
A little vegetable or corn oil for roasting
400-500g Swiss chard or cavolo nero or a mix, washed
2-3tbsp aged balsamic, mosto d'uva or pomegranate molasses
Preheat the oven to 220/gas mark 7. Season the beef fillet, heat an ovenproof pan on the stove with the vegetable oil and colour the fillet on a high heat on all sides; finish in the oven for 10-15 minutes, depending on the thickness but keeping it nice and rare.
While the beef is cooking, bring a pan of salted water to the boil. If using chard, slice or dice the stalks and cook until tender, drain, then cook the leaves until tender. Do the same for the cavolo nero but the leaves will take longer. Leave to cool a little in the colander and make sure there is no water left in the leaves. Cut the beef into 4 or 8 thick slices and place on the greens; spoon the balsamic or mosto around.