Preheat oven to 400 F (204 C) and line a baking sheet with parchment paper.
Place the cauliflower, onions, and (whole, peeled) garlic on the baking sheet. Drizzle with avocado oil and season with salt and pepper. Toss to fully coat the vegetables.
Place baking sheet in your preheated oven for 30 minutes, stirring halfway through.
While your veggies are roasting, place cashews in a bowl or measuring cup and pour over enough boiling water to cover them, then set aside. Then rinse and drain your can of white beans.
Remove your roasted veggies from the oven and immediately transfer them to a large stock pot or Dutch oven. Reserve a few pieces of cauliflower for garnishing, if desired. Add your rinsed beans, vegetable broth, water, and nutmeg to the pot and stir.
Heat over medium-high heat until it comes to a strong simmer, then reduce slightly and simmer on medium-low for 15-20 minutes, or until the cauliflower is very soft and falls apart easily when pierced with a fork.
Turn off heat. Carefully transfer mixture to a high-speed blender (that’s safe for hot foods), and add lemon juice and a pinch of salt. Blend soup until creamy and smooth. Pour half of the blended soup back into your pot, drain the cashews, and add them to the soup that’s remaining in the blender. Blend the cashews and soup until pale and creamy, about 1 minute. Pour the remaining soup into the pot and stir to swirl the two soup mixtures together.
Taste and adjust flavor as needed, adding salt and pepper to taste or more nutmeg for nuttiness. Serve and enjoy with a garnish of your reserved cauliflower, a sprinkling of parsley and red pepper flakes, pine nuts, and/or a swirl of olive oil (all optional).
Store leftovers covered in the refrigerator for up to 1 week, or in the freezer for up to 1 month. Reheat on the stovetop, adding dairy-free milk or broth as needed to thin.
*Nutrition information is a rough estimate calculated with DIY Vegetable Broth and without optional ingredients.