INGREDIENTS (4 servings):
2 large cucumbers, peeled
1/2 teaspoon sugar
2 onions, coarsely chopped
1 cup canola oil
3/4 cup dill fronds, plus more for garnishing
1 cup extra-virgin olive oil
1 tablespoon sunflower oil
1/2 pound chanterelle mushrooms, halved lengthwise if large
1 tablespoon finely chopped shallots
1 tablespoon finely chopped thyme
Freshly ground pepper
4 skinless halibut fillets (about 6 ounces each)
About 3 tablespoons fresh lemon juice
Edible flowers, for garnishing (optional)
1. Cut 1 of the cucumbers lengthwise in half. Using a small spoon, scrape out the seeds and add to a medium bowl. Cut the cucumber into 1/4-inch dice.
2. Coarsely chop the second cucumber and add it to the seeds. Sprinkle with the sugar and 1/2 teaspoon of salt and mix gently. Let stand for 10 minutes.
3. In the blender, puree the chopped cucumber mixture until smooth. Line a fine sieve with cheesecloth and set it over a bowl. Add the cucmber puree, transfer it to the refrigerator, and let drip for 2 hours.
4. Heat the oven to 375 degrees. In a shallow baking dish, stir the onions with the canola oil. Spread evenly over the bottom and cover with foil. Bake until the onions are soft and translucent, about 30 minutes. Remove from the oven and let cool.
5. Transfer the onions to the blender and puree, then scrape into a bowl.
6. Fill a medium bowl with ice water. In the blender, puree the dill with the olive oil at high speed until smooth. Scrape the dill oil into a small bol, set in the ice water, and refrigerate.
7. In a large saute pan, warm the sunflower oil over high heat. Add the mushrooms and cook, stirring frequently, until the water they release has evaporated, 3 to 4 minutes. Add the shallots and thyme, season with salt and pepper, and cook until the shallots are lightly browned, 1 to 2 minutes.
8. Bring 4 cups of water to a simmer in the bottom of a steamer. Season the halibut with salt and pepper and arrange on the steaming rack. Set the rack over the simmering water, cover and steam just until the fish is opaque throughout, 4 to 5 minutes. Transfer the halibut to a warmed platter and drizzle with some of the lemon juice.
9. Meanwhile, in a small saucepan, combine the diced cucumbers, 1 1/2 cups of the drained cucumber water, and 1 1/2 cups of the onion puree. Season with salt and pepper and bring to a simmer, then remove the pan from the heat. Whisk in 1/4 cup of the dill oil and season with lemon juice, salt and pepper. Briefly reheat the mushrooms.
10. Spread the cucumber sauce on warmed plates. Set a filet on each plate and spoon the mushrooms on top. Garnish with dill fronds and, if desired, flowers and serve.