Pour boiling water over the cashews and let them soak for 1 hour. After an hour, drain and rinse the cashews. Place the soaked cashews and water into a high-speed blender, along with the water, and blend until smooth and creamy. Set aside, as you will add this to your soup later.
Prep the mushrooms. Wipe off any dirt patches with a paper towel or clean kitchen towel. Depending on the variety of mushrooms, slice them or tear them with your hands.
Prep the leeks, starting by slicing off the dark green tops and discarding or saving for making vegetable broth. Cut each leek in half vertically and then slice horizontally, but not too thinly, as they’ll cook down with the mushrooms for quite a while.Note: Leeks are very dirty, so you need to wash them at this stage. Submerge chopped leeks in a bowl of cold water, run your hands through the bowl to loosen the dirt, and then scoop the leeks out using your hands or a slotted spoon. Pat the washed leeks dry. Heat a large sauté pan with deep sides (or a Dutch oven) over medium-high heat and add 1 ½ to 2 tablespoons of olive oil. Once the oil is shimmering, add half of the leeks and mushrooms. Cook for 8 to 10 minutes until mushrooms are nicely browned, stirring occasionally but not too frequently. You want the mushrooms to get a nice brown color.
Reduce the heat to medium and add half of the garlic, half of the thyme, and 1/4 teaspoon kosher salt. Cook for 2 to 4 minutes, or until the mushrooms are browned and crispy. When done cooking, transfer this batch to a plate or bowl.
Repeat the process with the remaining oil, mushrooms, leeks, garlic, thyme, and salt.
While the mushrooms are cooking, make the roux. In a medium bowl, whisk together the vegetable broth, tamari, Worcestershire sauce, and flour. Whisk until no clumps remain.
Pour the white wine into the pan with the cooked mushrooms and deglaze the pan by scraping up any brown bits on the bottom of the pan. Reduce the heat as needed to simmer for 3 minutes, or until the smell of alcohol has dissipated and the wine has mostly evaporated.
Pour the roux into your Dutch oven or sauté pan and whisk to combine, ensuring there are no clumps. Bring to a simmer, then pour in the cashew cream, tahini, nutritional yeast, ½ teaspoon kosher salt, and paprika. Bring to a simmer over medium-low heat. Cook for 10 minutes, until the sauce is thickened and very creamy.
Meanwhile, cook the pasta. Bring a large saucepan of salted water to a boil. Cook the pasta according to the package instructions until al dente. Drain and keep warm.
Stir the Dijon mustard into the stroganoff sauce and stir. Add the hot cooked pasta and chopped dill, and toss to coat. If you want to store this as leftovers, keep the pasta and sauce separate until you are ready to reheat them to eat.
Garnish your pasta with additional fresh dill or chives, and plant-based sour cream*.
Storage Instructions: Store the pasta and sauce seperatly in airtight containers in the refrigerator for up to 4 days.
Reheating Instructions: Heat gently on the stovetop over medium-low heat, adding a splash of water or plant-based milk to loosen the sauce as needed. You can also microwave it in short intervals, stirring in between, until warmed through.