Heat 15ml of olive oil in a frying pan.
Season the steak with salt and pepper and fry for 3-4 minutes per side.
Remove steak from pan and let it rest in a warm place.
Drizzle remaining olive oil over ciabatta and toast in a hot griddle pan.
Mix Stilton, butter, herbs, and lemon juice in a bowl until smooth.
Heat vegetable oil in a heavy-bottomed saucepan for frying.
Deep fry sweet potato slices until crisp and golden-brown.
Drain crisps on paper and season with salt and pepper.
Assemble sandwich by layering ciabatta, steak, and Stilton butter.
Serve the sandwich immediately with the sweet potato crisps.