For the steak sandwich, heat half of the olive oil in a frying pan. Season the steak with salt and freshly ground black pepper and fry for 3-4 minutes on each side, or until cooked to your liking. Remove from the pan and set aside to rest in a warm place.
Heat a griddle pan, drizzle the remaining olive oil over the ciabatta and chargrill until toasted on both sides.
For the Stilton butter, place all of the Stilton butter ingredients into a bowl and mix well until smooth.
For the sweet potato crisps, place the vegetable oil into a deep, heavy-bottomed saucepan and heat until a small cube of bread sizzles and turns golden when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Carefully place the sweet potato slices into the hot oil and deep fry until crisp and golden-brown. Remove from the oil with a slotted spoon, drain on kitchen paper and season with salt and freshly ground black pepper.
To serve, place one slice of ciabatta onto a serving plate and top with the steak and the Stilton butter, then the remaining piece of ciabatta. Serve the sweet potato chips alongside.