Oysters, roast tomatoes, celery, dashi jelly and chillied sesame dressing

I love this salad served icy cold, made with freshly shucked oysters. However, I’ve also served it in cooler months using oysters that I’ve poached briefly in a mixture of dashi and cream. To do that, make double the quantity of dashi given here and combine half of it with an equal amount of coconut milk or cream. To set the jelly, I use agar powder, which is a seaweed-based ‘vegetarian gelatine’, but you can replace it with regular gelatine. The dashi stock makes more jelly than you need b