Preheat the oven to Gas Mark 4, 180°C (350°F).
Place a large piece of cling film onto the work surface and lay half the streaky bacon rashers on top. They should be perpendicular to the edge of the counter and slightly overlapping. Season a pork steak and lay it on top of the rashers. It should be parallel to the counter. Place half the sage leaves on top of the pork. Then roll up using the cling film to help you to make a tidy, tight roll. Repeat with the remaining rashers, pork steak and sage leaves.
Transfer the pork to a lightly oiled roasting tin with the loose ends of the bacon tucked underneath.
Brush the bacon all over with a little oil. Place the pork in the middle of the oven and roast for approximately 35 minutes. If you are using a meat thermometer it should read 65°. When the meat is done, take it out of the oven, remove from the roasting tin. Wrap it loosely in tin foil and let stand 5-10 minutes while making the sauce.
Meanwhile add the shallot to the juices in the roasting tin and sauté over a gentle heat. Take the dried mushrooms from the soaking liquid and chop into small piece. Reserve the liquid to add to the sauce. Add the dried and fresh mushrooms to the roasting tin and cook until lightly browned. Add in the sherry, white wine or lemon juice, the porcini soaking liquid and the cream. Allow to simmer down to make a thick, creamy sauce.
Mash the celeraic and potatoes with a little butter and seasoning. Slice the pork and serve it with the sauce, celeriac and potato mash and tender stem broccoli.