1 (2 1/2 pound) kabocha squash
3/4 pound turnips, about 3 medium-sized turnips
3/4 pound celery root, about 1 medium-sized celery root
1 1/2 tablespoons olive oil, divided, plus more for drizzling over each serving (optional)
Sea salt, as needed
A few fresh rosemary leaves
2 to 3 cups light vegetable broth
2 to 3 tablespoons fresh lemon juice, or to taste
Hot paprika or cayenne pepper, to taste
3 tablespoons pure maple syrup, plus more to taste
3 tablespoons unsalted butter
3/4 cup chopped pecans, lightly toasted
Heat oven to 400 F. Cut the kabocha squash in half with a very sharp knife, scrape out seeds and strings, and place halves cut-sides down on a lightly oiled, nonstick baking sheet. Peel the turnips and cut them into wedges. Peel the celery root and cut it into 1-inch pieces. Toss turnips and celery root with about 1/2 tablespoon of the olive oil and a pinch of the sea salt and spread them on another baking sheet.
Roast all prepared vegetables in hot oven until squash gives easily when poked with a wooden spoon, and turnips and celery root are tender and flecked with dark brown, about 40 minutes to an hour. Remove pans from oven. When squash is cool enough to handle, scoop it out of its shell.
While vegetables are roasting, cut the leeks in half lengthwise, wash them thoroughly and slice them crosswise very thinly (both white and light green parts); you should have about 1 1/2 cups. Set leeks aside. Peel and chop the onion and set it aside.
In a large soup pot, heat remaining tablespoon oil over medium heat. Add onions with a dash of salt and the rosemary and cook, stirring now and then, until soft and golden brown, 10 to 12 minutes. Stir in roasted squash, turnips, celery root and leeks with 4 cups water and 1 teaspoon salt. Simmer vegetables, covered, about 20 minutes to let them get perfectly soft. Stir in 2 cups of the vegetable broth, 2 tablespoons of the fresh lemon juice, a pinch of hot paprika or cayenne and the maple syrup. Remove from heat.
Allow soup to cool somewhat, then puree it in a blender, in batches, or in pot with an immersion blender. Add a little more vegetable broth if soup is too thick to pour easily from a ladle. Return soup to a clean pot and bring it back to a simmer.
Meanwhile, in a small saucepan, melt the butter over medium heat. Lower heat and keep cooking butter for a few minutes, stirring with a whisk, until it is a light golden-brown. Stir browned butter into soup.
Taste soup and correct seasoning, whisking in more salt, lemon juice or maple syrup as needed. Sprinkle each serving of soup with a spoonful of toasted, chopped pecans and a drizzle of olive oil if desired.
Makes about 10 cups soup.
— Recipe adapted by the Los Angeles Times from "Love Soup," by Anna Thomas.