From Sarah Britton's "Naturally Nourished" cookbook: "The process for this soup is incredibly easy: all the ingredients are placed on a rimmed baking sheet, and the oven does the work. There isn’t even a pot to wash when the meal’s over. You can use this procedure with any veggies, plus onions and garlic. Just add everything to a blender directly from the oven, pour in some hot vegetable broth, and dinner is served. Bam!"
Preheat the oven to 400° F (200° C). Slice off the stem of the garlic bulb and the portion just below the stem, revealing the open cloves. Spread the coconut oil on top, wrap the bulb tightly in aluminum foil, and set it on a rimmed baking sheet. Roast for 15 minutes.
While the garlic is roasting, peel and roughly cut the parsnips into similarly sized chunks to ensure even roasting. Chop the onions. After the garlic has roasted for 15 minutes, add the parsnips and onions to the baking sheet. Roast until tender, about 30 minutes.
Add the roasted parsnips and onions to a blender. Remove the foil from the garlic and squeeze the bulb from the bottom to extract the cloves into the blender. Add the broth, beans, salt, olive oil, and lemon juice, and blend on the highest setting until the soup is smooth and creamy. Transfer the soup to a stockpot and heat until steaming, if necessary.
Serve hot with a drizzle of olive oil and some black pepper and parsley, if using.