Make a deep longitudinal cut in each pork fillet without piercing through.
Place sliced Stilton and sage leaves inside the cut.
Close the fillets, tie with string in several places, and season with salt and pepper.
Heat butter and oil in an ovenproof dish on the hob until lightly browned.
Lightly coat the fillets in flour and sauté on both sides until browned.
Add white wine to the dish and bring to a boil.
Roast in a preheated oven at 200°C for 30 minutes.
Remove from oven, discard string, and slice into 1cm pieces.
Deglaze the dish with 15ml of water to create a sauce from the pan drippings.
Pour the sauce over the sliced pork and serve immediately.