Jamie Oliver's advice and seared the fillet first. He was rather concerned about this, but I thought it was a great idea. The beef would still 99% raw, but you get the divine flavour from searing it which simply does not exist with the fully raw one. If you want to get technical, read this about the 'Maillard' reaction which goes to some lengths to explain why you sear meat for a casserole, why it tastes good, and why it is important.
Or you could just cook take a very decent fillet of beef (you only need a little per person so no need to go overboard, Dad), rub a little olive oil all over it, season really well, and sear on all sides in a very hot pan, no need to add any more oil as you've oiled your beef already. If the pan is hot enough it should only take a minute or two per side, you want a deep golden brown colour all over. Slice as thin as you can and serve on a pretty place, sprinkled with shaved fennel, a little grated orange zest, rocket, shaved Parmesan, a dribble of extra virgin olive oil and a little more salt and pepper.
Searing the beef makes it much less 'scary' even though it is still essential raw. The searing troubled Dad for some reason, he couldn't slice the beef as thinly as when it's all raw and semi frozen (helps you slice it thinner as it stays firm), but I can't see the harm in freezing it once seared and then slicing it.
What Dad should have been worried about was how much his head would hurt the next day, after staying up well past his bedtime with my Godfather, un-supervised, with a bottle of brandy. The beef was delicious, his hangover was not.