Start by chopping all the vegetables.
Peel and chop the carrots and parsnips. Place them on a cookie sheet, drizzle with olive oil, and sprinkle a bit of sea salt. Roast in the oven at 425°F until they become soft and develop lightly caramelized edges. This will take approximately 45 minutes.
While the vegetables are roasting, melt butter in a heavy-bottomed soup pot. Add the onions and cook until they become soft. Stir in the minced garlic and cook for about 60 seconds.
Pour in the vegetable stock, cannellini beans, harissa paste, lime juice, salt and pepper, cayenne pepper, and nutritional yeast (if using). Bring the mixture to a light simmer and let it cook while the vegetables are roasting.
Once the roasted vegetables are ready, add them to the soup pot and turn off the heat. Pour in the coconut milk and let the soup cool for around 20 minutes, until it's safe to blend.
Blend the soup using either a blender or an immersion blender. Depending on the power of your blender, you might need to blend in batches. Don't forget to rinse out the empty soup pot.
Return the blended soup to the pot and gently reheat it. Take a taste and adjust the seasonings as needed. Add more salt, pepper, harissa, or lime juice to suit your preferences.
Serve the soup hot, garnished with fresh basil and a drizzle of olive oil.