How can I perfectly roast a small (one pound) piece of beef?

[AbsentmindedWoman]

I'd normally do 15 mins per pound plus 20 mins in addition. With a small lump though, will this still work?

I have 2lb but it's only me eating it, so want to freeze the other half.

What cut is it?

If you like it pink I would give it a brief sear in a very hot pan just to brown it, then stick it in the oven for 30 minutes. Hard to say really without seeing what shape it is?

Or maybe only 20 minutes??

It's silverside - so have concerns about it turning into old leather!

Would 30 mins really be enough? While I prefer rare for a roast dinner, I want this on the more medium side of rare because I'm planning to use it cold for lunches.

Spent so long dithering over different ways to cook it I'm going to be bloody starving by the time I have lunch now!