Rub the steak with olive oil and season with salt and pepper.
Sear steak in a smoking hot pan for 3 minutes per side or longer for well-done.
Remove the steak and add onions to the pan.
Caramelise onions over a gentle heat.
Place bread on a plate and top with onions and steak.
Cook grated carrot and vinegar until liquid reduces to 15ml.
Stir in spices, honey, and tomato purée and cook until jammy.
Spoon the chutney onto the steak sandwich.
Heat vegetable oil in a saucepan until a bread cube sizzles and browns.
Thinly slice celeriac with a mandolin and dry with a towel.
Fry celeriac slices in oil for 4 minutes until golden.
Drain crisps on paper, salt them, and serve with the sandwich.