The beech mushrooms are less the stars here and more of a textural element used as a garnish. Because of this, it’s extra important to use homemade mushroom stock to highlight the mushroom flavor. This soup started in my mind’s eye somewhere in Thailand (lime leaves, basil) and then — somewhat inexplicably — migrated to West Africa (sweet potatoes, peanuts). This is the perfect kind of soup to serve when it’s raining, you’re snuggled up on the couch with a blanket, a fire is lit, Thai music is playing, and a zebra is running through your living room. — Becky Selengut, Shroom
You can purchase whole dried chiles, toast them in a dry pan until flexible and fragrant, and then buzz them in the food processor, or just use regular bottled red pepper flakes.
Recipes from Shroom: Mind-bendingly Good Recipes for Cultivated and Wild Mushrooms by Becky Selengut/Andrews McMeel Publishing, LLC.
Preheat the oven to 400 degrees F.
Drizzle a little high-heat oil on a rimmed baking pan. Throw the shiitakes, along with the chopped-up onion, onto the pan, and toss with the oil. Roast until caramelized, about 20 minutes. Deglaze the pan with a little wine or water, scraping up any brown bits stuck to the pan. Dump the mushrooms and onions, along with the liquid, into a stockpot along with the contents of that freezer bag (no need to thaw) and a few rehydrated pieces of dried porcini (along with the strained soaking liquid). Cover with 3 quarts water, chuck in about 5 peppercorns, bring to a boil, lower to a simmer, and cook, uncovered, for 45 minutes.
Pour the contents of the pot through a fine-mesh strainer set over a large bowl, pressing on the solids to extract as much liquid as possible. You should end up with about 2 quarts mushroom stock.
You can find many varieties of bottled chile oil in Asian markets or online, but it’s ridiculously easy to make a batch from scratch and store it in your fridge. Plus, your homemade oil contains none of the additives and preservatives that are commonly added to the bottled versions. To make your own, in a small saucepan set over medium heat, combine 1 cup peanut or coconut oil, along with 3 to 5 tablespoons red pepper flakes (The quantity will depend on how hot you want the oil to be.) Heat the oil to 300 degrees F on an instant-read thermometer. Remove the pan from the heat and try not to breathe in the fumes!
Let the oil cool to 250 degrees F, and then add 1 tablespoon toasted sesame oil and 2 tablespoons minced roasted unsalted peanuts. Transfer to a clean glass jar with a tight-fitting lid. Add 1 teaspoon salt and 1 teaspoon sugar. Seal the jar, shake it a few times to distribute the ingredients, and leave at room temperature for 2 days. Refrigerate. It will keep for at least 1 month, if not longer, in the fridge.
moment, add the onion and ¼ teaspoon of the salt and sauté for 10 minutes, until starting to brown. Add the sweet potatoes and lime leaves. Sauté for 2 to 3 minutes, then turn the heat to high, add the wine, and deglaze the pan, scraping up any brown bits. Add the stock, bring to a boil, and then lower the heat to a gentle simmer. Cook until the sweet potato cubes are tender, 20 to 25 minutes.
Add the vinegar. Remove the lime leaves. Pureé the soup in a blender until very smooth, or pureé in the pan using an immersion blender. Season with the fish sauce, another ¼ teaspoon salt, and more rice vinegar. If you feel it needs more salt, add more fish sauce (a little at a time). Keep tasting until it’s right for you.
Meanwhile, prepare the beech mushroom mixture. In a large sauté pan over high heat, melt the remaining 1½ tablespoons of coconut oil. After a moment, add the mushrooms and the remaining ¼ teaspoon salt. Toss the mushrooms around in the oil, and then spread them out. The idea is to get them to release their liquid and brown quickly. When they brown, stir in the basil and peanuts and transfer to a small bowl.
Serve the soup in wide bowls, garnished with the mushroom mixture and drizzled with some chile oil.