Perfect roast beef and sides

[Sundaychiller]

I am cooking a 1.5kg piece of topside for guests today. Anyone got a fool proof recipe with timings please as I dont have a thermometer.
Also how do you keep parsnips, cauliflower cheese etc hot when cooking Yorkshire puds.
Thanks for your help!

20 minutes at gas mark 9, then 15mins per 450grammes for rare, 15 minutes extra for medium rare. (Delilah Smith) I always take it out a bit early, think my oven is extra hot. Take beef out, cover in foil/cloth, leave on top of hob. Put in yorkshires/parsnips on highest heat, will take about 25 mins if you’ve cut the parsnips thinly or parboiled them. I juggle things in the oven or use dishes that’ll fit everything.

@Cherrysoup thanks for your help!