2 tbspmanzanilla sherry2 tbspcaster sugar200 gmpiece of sashimi-grade tuna200 gmassorted mushrooms, such as king brown, Swiss brown and button, very thinly sliced½bunch of chives, cut into 10cm lengthsTo serve:lime wedges and extra-virgin olive oil
Combine sherry, sugar and 2 tbsp fine sea salt in a non-reactive dish. Add tuna, turn to coat, cover with plastic wrap and refrigerate until cured (24 hours). Scrape curing mix from tuna and thinly slice.
Place mushrooms and chives on plates, top with tuna, season with freshly ground black pepper, squeeze over lime juice, drizzle with extra-virgin olive oil and serve.