Yotam Ottolenghi and Ramael Scully's Pistachio and Pine Nut-Crusted Halibut

For the pistachio and pine nut crust:

• 10 tablespoons (150 grams) unsalted butter, cut into 1/3-inch dice
  
• 2 ounces (60 grams) shelled pistachios, lightly toasted and coarsely chopped
  
• 2 ounces (60 grams) pine nuts, lightly toasted and coarsely chopped
  
• 1/4 teaspoon superfine sugar
  
• 2 tablespoons lemon juice
  

1. Place the butter for the nut crust in a medium saucepan over medium-high heat. Cook for 4 minutes, until the butter is nutty smelling and golden brown. Remove from the heat and strain the butter through a fine-mesh sieve to remove any black bits.
2. Add the pistachios, pine nuts, sugar, lemon juice, and 1/4 teaspoon salt. Mix well, then spread out in a small parchment-lined baking sheet, about 6 inches wide and 8 inches long. Chill in the fridge for 2 to 3 hours, until the butter has set firmly, then cut the mixture into 6 equal rectangles. Return the rectangles to the fridge until ready to use.

For the wild arugula and parsley vichyssoise and the halibut fillets:

• 3 1/2 ounces (100 grams) parsley stems and leaves
  
• 5 1/4 ounces (150 grams) wild arugula
  
• 3 tablespoons olive oil, divided
  
• 3 tablespoons (40 grams) unsalted butter
  
• 2 medium shallots, coarsely chopped (3 1/2 ounces/100 grams)
  
• 3 cloves garlic, crushed
  
• 1 medium leek, green and white parts finely sliced (7 ounces/200 grams)
  
• 2 large all-purpose potatoes, peeled and cut into roughly 3/4-inch pieces (13 ounces/370 grams)
  
• 4 1/2 cups (1 liter) chicken stock
  
• 1 ounce (26 grams) spinach leaves
  
• 6 halibut fillets, skinless and boneless (1 pound 14 ounces/950 grams)
  
• 2 tablespoons lemon juice
  
• 12 breakfast radishes, green leaves and roots left on and sliced in half lengthwise (or 8 round radishes)
  
• Coarse sea salt and black pepper
  

1. To make the vichyssoise, bring a medium saucepan of salted water to a boil and add the parsley and arugula leaves. Blanch for 30 seconds, then refresh under cold water. Strain, squeeze out the excess water, set aside to dry, then coarsely chop.
2. Place 1 tablespoon of the oil and the butter in a medium saucepan over medium heat. Add the shallots and sauté for 4 to 5 minutes, stirring once or twice, until soft but not colored. Add the garlic and leek and cook for another 2 to 3 minutes. Add the potatoes and cook for 5 to 6 minutes, stirring frequently, until shiny and glossy.
3. Pour over the chicken stock and bring to a boil over medium-high heat, then simmer for 8 to 10 minutes, until cooked by still retaining a bite. Add the blanched parsley and arugula and cook for a final minute, then remove from the heat and add the spinach, along with 1 1/2 teaspoons of salt and a good grind of black pepper. Transfer to a blender, blitz well until completely smooth, and set aside until ready to use.
4. Preheat the broiler to 400° F or to its highest setting. Spread the halibut fillets out on a large parchment-lined baking pan and brush them with the remaining 2 tablespoons of oil. Season with 1 1/2 teaspoons of salt in total and a good grind of black pepper and cook for 6 to 7 minutes, until the halibut is almost cooked. Remove the baking pan from under the broiler and lay a rectangle of nut butter on top of each fillet. Return to the broiler and cook for a final 2 to 3 minutes, until the crust is golden brown. Remove from the oven and squeeze over the lemon juice.
5. Warm the vichyssoise and spoon it into shallow wide bowls. Lay a halibut fillet on top, place the radish pieces alongside, and serve at once.