What I had for dinner tonight...
Beef filet - (use a nice piece of center cut)
Parmesan cheese (Grana Padano)
Olive Oil - (Extra Virgin Olive Oil - cold pressed)
Put the beef into the freezer for 30 minutes to firm it up and make it easier to slice.
Use a very sharp, large knife, cut slices as thinly as you can. Lay these on a plate and cover them with clingfilm as you cut to stop them colouring. If you put a layer of baking parchment or clingfilm between the layers you'll easily be able to separate them out easily later.
To serve, plate the beef slices on a platter or individual plates, heap some parmesan shavings in the middle and drizzle the olive oil around the edge.
There are some recipes that add other ingredients to it, like lemon juice, mustard, salt and pepper, but I prefer the "simple version", especially when made from best quality/organic beef and olive oil.