I have also made this delicious recipe several times after first seeing it on the Nigella Bites tv show. I have successfully used granulated sugar in place of caster sugar with no problems. Also, when fresh peas are out of season, this is still delicious using frozen peas. This is an easy to prepare, tasty and elegant salad. One note: On the tv show, Nigella used "baby gems" in place of mixed greens - which are mini romaine lettuce heads(you could also use "hearts of Romaine"), which she tore up into chunks, but the mixed greens Kylie suggests above are obviously good as well. Chicory is also known as "Belgian Endive."
Lovely salad. I will try this next time with some feta as well.