* 2 tbsp coriander oil
* portion of wasabi lemon cream
* 2 x 20cm (7.in) diameter wheat-flour tortillas
* 2 tbsp olive oil
* a sprinkle of Maldon sea salt flakes, plus extra to garnish
* pink grapefruit, peeled
* 150g sushi-grade tuna
* ½ small avocado, cut into 1cm cubes
* 2 tbsp finely diced red onions
* 4 tsp tobiko eggs (fish roe)
* red chilli, deseeded and finely chopped, plus 2 slices to garnish
* a few baby coriander leaves, to garnish
* 1 tsp toasted white sesame seeds, to garnish
* a sprinkle of shichimi pepper, to garnish
For the the coriander oil:
Makes about 300ml
* 100g coriander stalks and leaves
* 300ml sunflower oil
For the wasabi lemon cream:
* 5 tbsp Japanese mayonnaise (or regular)
* 5 tbsp soured cream
* 1 tbsp wasabi paste
* a few drops of lemon juice
* a pinch of salt
1. First make the coriander oil. Wash the coriander, pat dry on tea towls and then roughly chop.
2. Heat the chopped coriander and sunflower oil in a small pan over a very gentle heat; warm the oil through until it’s lukewarm and the coriander has wilted, for about three minutes. Take off the heat, place the pan in a bowl of iced water to cool down quickly and retain its vibrant green colour.
3. Once cool, blend the oil and coriander in a food processor until smooth. Transfer the coriander and oil mixture to a bowl, cover it and let it infuse in the fridge for two hours, or anything up to 48 hours.
4. Strain the mixture through a fine sieve or a paper coffee filter into a sterilised jar and store in the fridge, where the oil will keep for up to four weeks.
5. Next, make the wasabi lemon cream. In a bowl, whisk all the ingredients together until well combined. Check the seasoning and add more salt, wasabi paste (if you like it a tad spicier) or lemon juice. The wasabi cream should taste spicy, but not overly so, with a refreshing acidity from the lemon. Once made, this cream lasts a week in the fridge.
6. Preheat the oven to 200C/400F, and line a baking tray with non-stick baking parchment. Prick the soft tortillas to stop them from bubbling up during baking.
7. Brush the tortillas on both sides with olive oil, sprinkle a little sea salt over them, cut each tortilla into equal quarters, cover with a tray (to help flatten the tortillas as they cook) and bake for two to three minutes until lightly coloured.
8. Turn over and bake again. Remove from the oven and transfer to a wire rack; they will crisp up further as they cool down.
9. Meanwhile, prepare the other ingredients. You’ll need to extract the pink grapefruit flesh gently from its segments to make 1–2cm triangular pieces. Set aside.
10. When you are just about ready to serve the tostadas, cut the tuna using a very sharp knife into thin slices.
11. Place the crispy tortilla quarters on a serving plate, close together as if the tortilla was still whole. Spoon half of the wasabi lemon cream over the tortillas. Place the thin slices of tuna over the tortilla pieces and cream. Spoon the remaining wasabi lemon cream over and around the tuna.
12. Now scatter the pieces of grapefruit, the cubes of avocado, the finely diced red onions, the tobiko eggs and red chilli over the surface of the tortilla.
13. Drizzle the coriander oil over the white cream, scatter a few small leaves of coriander and a slice of red chilli in the middle of the plate. Finish off with a sprinkle of toasted sesame seeds, a dusting of shichimi pepper and some Maldon sea salt flakes and serve.
More from Nikkei Cuisine:
- Scallops with black quinoa tabbouleh and candied kumquats
- Flourless chocolate cake with Armagnac prunes
Nikkei Cuisine - Japanese Food the South American Way by Luiz Hara and published by Jacqui Small is out now, £25