Pulse the cauliflower florets in small batches in the bowl of a food processor until the size of grains of rice. Set aside.
Heat the oil in a large skillet. Add the leeks and a sprinkle of salt and saute until softened. Add the garlic and saute a few minutes more, until fragrant. Add the optional vegetables, first adding those that will take longer to cook, then any others.
Meanwhile, in a separate bowl whisk together the tahini, nutritional yeast, miso paste and broth. Set aside.
When the leeks are tender and the other vegetables almost done, add the cauliflower. Cook for a few minutes more, then add the broth mixture and simmer for a few minutes more to thicken.
Remove from heat and stir in the lemon juice. Adjust the seasonings and serve garnished with parsley. (Recipe♦247)