Make a deep cut in each pork fillet but not all the way through. Slice the Stilton and place in the cut together with the sage leaves. Close the fillet and tie with string in 2 or 3 places. Season.
Heat the butter and oil in an oven dish on the hob. Lightly flour the fillet, remove any excess. When the butter and oil are hot and lightly brown, sauté the fillet on both sides. Add the wine and bring to the boil. Place in a preheated oven at 200C/400F/Gas 6 for 30 minutes.
Remove from the oven, cut away the string and slice the meat into 1cm/½in pieces and keep warm.
Taste the cooking juices and adjust the seasoning. Add a tablespoon of water to the dish and scrape the tasty bits off the bottom to make a sauce. Place the sliced pork on plate and pour over the sauce. Serve with baby cabbage.