To make the French curry sauce, begin by adding a few tablespoons of sunflower oil to a pan. Cook the onions over mediumlow heat to sweat, avoiding color. After 5 minutes of cooking, add Espellete pepper, tomatoes and garlic, and continue to cook on low heat. With the ingredients still in the pan, add the white wine to deglaze. Stir slowly for a few minutes for the wine to cook down.
When the wine is almost evaporated, add the curry spice blend and allow to cook for 5 more minutes. Next, add the makrut lime leaf, clam juice, water, coconut water and sweet potato. Bring to a boil, then simmer covered for 45 minutes. Add mushrooms, cabbage, basil, cilantro (reserve a few pieces for a garnish) and cream. Simmer for 20 minutes. Add salt to taste.
Meantime, preheat oven to 350º F. In a separate pan, add a few tablespoons of sunflower oil and heat. Slice halibut into individual portions and sear with skin side up until top is golden brown. Turn halibut into an ovenproof pan, top with 1 tablespoon of butter and bake for 7 minutes.
Swirl lemon juice into the curry. Plate and garnish with carrots and cilantro.