Peel potatoes and slice very thinly. Rinse under cold water until the water runs clear, then dry thoroughly between two clean tea towels.

Heat oil in a deep saucepan and fry potatoes in batches until golden and crisp. Drain on paper towel and season with salt. Set aside.

Cut steak into small bite-sized chunks. Season with salt, milled pepper and Cajun seasoning, if using. Heat vegetable oil in a large frying pan over high heat and fry steak in batches until golden brown and cooked to your liking. Set aside.

For the blue cheese sauce, combine blue cheese, sour cream and milk in a bowl. Mix until well combined but still slightly chunky. Season to taste.

Arrange potato chips on a serving platter and scatter the cooked steak evenly over the top.