Pour some boiling water to cover the cashews while you prep everything else - about 15 minutes. Drain before using.
Heat the olive oil in a large Dutch oven or soup pot over medium to medium-high heat. Once hot, add the leeks. Sauté until they are softened and starting to brown, 3-4 minutes. Add garlic, thyme, oregano, and red pepper flakes (if using), and cook for 1 minute, stirring frequently.
Pour in the vegetable broth and deglaze the pot, stirring up any browned bits on the bottom of the pot. Then add the soaked and drained cashews, cauliflower florets, and 1 1/2 teaspoons kosher salt black pepper to taste. Add enough water to cover the cauliflower (I added 1 cup or 240 mL, but you can add more if you want a thinner, soupier texture).
Bring the soup to a boil. Then reduce the heat to maintain a rapid simmer and cook for 15 minutes, or until the cauliflower is tender and soft.
While the soup is simmering, chop the kale into thin strips. Set aside.
Also meanwhile, heat a large skillet over medium heat. Once hot, crumble the vegan sausage into the pan and stir around occasionally, until the sausage is browned. Or, if you’ve sliced your sausage, cook until seared on both sides. Remove from the heat and set aside.
Once the soup is done cooking, blend it up until thick, creamy, and smooth. You can transfer it to a stand blender (in two batches), or use an immersion blender. If you use a stand blender, remove the center cap of the blender and cover it with a dish towel to allow the steam to escape.
Return the pureed soup to the soup pot and bring it back to a simmer. If it is too thick for your liking, add more water to thin. Add the sliced kale and browned sausage, and simmer until the kale is tender and wilted, about 3 minutes. Squeeze in some lemon juice, if using. Taste for seasonings, adding more salt and pepper as needed.
Serve each soup bowl with a drizzle of extra virgin olive oil, and if desired, fresh thyme and parsley.