Beef Stuffed with Leek Spinach & Feta

¼ cup rice bran oil
1 leek, white only, sliced
3 handfuls spinach leaves, trimmed
80 g feta
1 kg beef fillet, trimmed of fat & sinew
1 tsp SIDS CRAZY SALT
1 tbsp flour
125 ml port
80 ml red wine
1 cup beef stock
1 kg kumera, peeled & cut in chunks
100 g butter, chopped
SIDS SALT & PEPPER to taste

Preheat oven to 200°C. Heat ½ the oil in a saucepan over a low heat the fry the leek until soft but not coloured. Set aside. In a wok, add spinach and stirfry until just wilted. Squeeze out excess water then coarse chop. Combine the leeks, spinach and feta then season with SIDS SALT & PEPPER to taste.
Cut a 2 cm deep pocket down the side of the fillet and spoon in the feta mixture. Close and secure with string at 10 cm intervals. Spray with oil then sprinkle with SIDS CRAZY SALT.
Heat the remaining oil in a large frypan over a high heat and brown the beef all over. Transfer to a roasting dish, along with any pan juices and roast for 30-40 minutes, depending on thickness, to medium-rare. Remove the beef to a board and set aside to rest in a warm place, loosely covered, for about 10 minutes. Transfer the roasting pan to the stovetop over a low heat and stir the flour into the pan juices. Whisk in port, wine and stock. Season, then increase the heat to medium then simmer and stir for 5 minutes until smooth.
Meanwhile, cook the kumera in a large pot of salted water until tender. Drain, then add butter and blend until smooth, then season to taste.
Divide kumera mash among the serving plates. Top with slices of beef then drizzle with the pan juice mixture.