2 1/2cups chopped white onions (about 2 small onions)
2heads cauliflower, greens removed
2pounds parsnips (about 4 medium-large), peeled and ends trimmed
3sprigs fresh thyme, plus leaves for garnish
2tablespoons extra virgin olive oil, plus more for garnish
1cup heavy cream
salt and freshly ground black pepper, to taste
Preheat the oven to 400 degrees F.
In a heavy-bottomed large dutch oven or stock pot, melt the butter over medium-low heat. Add the chopped onions and sweat, stirring occasionally, until translucent and just beginning to brown on the edges, about 10 – 15 minutes.
While the onions cook, prepare the cauliflower and parsnips: remove the greens from the stems of the cauliflower and cut the stems into 1-inch sized chunks. Separate the heads into florets. Reserve 2 heaping cups of the florets and set aside. Add the rest of the cauliflower to a large bowl. Peel the parsnips and cut into 1-inch sized pieces. Add the parsnips to the bowl with the cauliflower.
Once the onions are translucent, add the parsnips and cauliflower and increase the heat to medium. Cook for 15 minutes, until vegetables are just beginning to brown on the edges. Add 8 cups of water, the thyme sprigs, and bay leaves. Bring to a boil over high heat, reduce to a simmer, and simmer, uncovered, for 45 minutes.
While the soup is simmering, prepare the garlic and roasted cauliflower garnish: Separate the reserved 2 heaping cups of florets into even smaller florets. Spread evenly in one layer on a sheet pan. Cut the garlic heads in half horizontally, keeping the peels on, and arrange next to the cauliflower. Drizzle everything with 2 tablespoons of olive oil and ½ teaspoon of coarse salt. Transfer to the preheated oven and roast. After about 25 – 30 minutes, once cauliflower is browned, remove from the pan and set aside. Allow garlic to continue roasting for an additional 10 – 15 minutes until soft and browned on the edges. Remove from the oven and allow to cool.
Once soup has simmered for 45 minutes and the vegetables are tender, remove from heat. Carefully remove the bay leaves and sprigs of thyme (the leaves will have fallen off by this point) and discard. Squeeze the roasted garlic from the peels into the soup, being careful not to get any peels into the pot. Working in batches, or with an immersion blender, puree the soup until completely smooth. If using a blender, transfer the soup back to the pot after its pureed to rewarm.
Add the heavy cream and adjust the seasoning to taste (I added 3 teaspoons of salt and a few cracks of black pepper). If soup is too thick for your liking, you can add a bit of water at this point (though I didn’t need to).
Serve the soup in bowls and drizzle with extra virgin olive oil. Sprinkle roasted cauliflower florets and thyme leaves over the top as garnish.