Sweet beetroot pickle

My mum is British; she was born and grew up in north London. The food I cook these days is far removed from the food she grew up with, nonetheless this is her recipe. I think it originally came from a Jewish cookbook she got when she went to Israel for the summer as a teenager and found herself in a camp in charge of cooking for another 30 hungry teenagers. The original called for boiling the beets in water until soft, but we prefer to roast ours, as in the following recipe.