Preheat the oven to 200C/400F/Gas 6.
Heat the oil in an ovenproof frying pan. Add the lamb and cook for 1-2 minutes on each side.
In a bowl mix together the breadcrumbs, Dijon mustard and parsley. Place the breadcrumb mixture onto each piece of lamb, then transfer to the oven to bake for 4-5 minutes, or until cooked through. Remove from the oven and leave to rest for 3-4 minutes.
For the creamy leeks, heat the oil in a frying pan, Add the onion, leek and garlic and fry for four minutes.
Add the cream, Stilton and white wine and cook for five minutes, or until the Stilton has melted and the cream sauce is thick.
For the port sauce, heat the beef stock and port together in a small saucepan. Bring to the boil and cook for five minutes, then add the butter and stir in to melt.
To serve, place the creamy leeks into the middle of a plate. Top with the lamb and drizzle the port sauce all over.