Pre-heat the oven to 160°C/320°F and prepare the sirloin by lightly coating the roast in olive oil and seasoning well with salt and freshly ground black pepper.
Pour a splash of oil in a hot pan and lightly brown all sides of the roast, including the ends, to seal the meat and lock in the juices.
Place the beef in an oven-safe dish, cover with tinfoil and roast in the oven for 40 minutes for a medium-rare roast beef.
Put a medium saucepan of salted water on the boil and cook the potatoes for 15 to 20 minutes or until you can easily push a knife through them.
To make the dipping sauce, combine the yoghurt with the Chipotle Tabasco sauce, adding more or less depending on how spicy you would like the sauce. Season well with salt and refrigerate until needed.
Drain the water from the saucepan and add the butter and milk to the potatoes. Using a potato masher, mash potatoes until smooth and creamy.
Remove the sirloin from the oven and allow to cool slightly. Using two forks or your hands, pull the beef apart to create a shredded texture.
In a bowl, combine the shredded beef with the mashed potatoes, dijon mustard, parsley and diced gherkins and divide the mixture into equal parts and roll each piece into a ball, then form into small flat patties.
One at a time, coat each hash cake in the flour shaking off the excess, then dip into the egg and then finally coat well with the panko breadcrumbs.
Heat a few tablespoons of olive oil into a large frying pan over a medium-high heat and fry the hash cakes for about 4 to 5 minutes on each side or until golden brown. Serve with the chipotle mayo and a fresh herb salad.