This lemony roasted cauliflower soup is simple and comforting, the cauliflower flecked all over with roasty-toasty bits, the garlic cooked until sweet and soft, with a kiss of warm spices brightened with lemon at the end. It’s basically perfect.
CHOP: Preheat the oven to 425 F / 220 C. Set out two half sheet size rimmed baking sheets. Remove the greens and stems from the cauliflower heads and discard. Cut the cauliflower into florets and divide between the two sheets. Drizzle each of the sheets with 15 milliliters / 1 tablespoon of the olive oil and sprinkle with salt, tossing to coat evenly.
ROAST: Slice the stem from the top of the garlic, exposing a little of each of the garlic cloves, and discard it. Wrap the garlic with foil and nestle it into the middle of one of the sheet trays. Roast on the lower and middle racks of the oven until the cauliflower is tender and browned at the edges, about 30 – 40 minutes. Depending on your oven, you may need to rotate the sheets for even cooking. Once done, remove the trays from the oven, unwrap the garlic and discard the foil; set aside to cool.
SOFTEN: Add the remaining 15 milliliters / 1 tablespoon of the olive oil to a large 6.5 quart dutch oven over low medium heat, along with the diced onion. Cook, stirring occasionally, until the onion softens but does not brown, about 10 minutes or so.
BLEND: Transfer the softened onion to the pitcher of a high powered blender. Add half of the roasted cauliflower and as much broth as will fit safely in your blender pitcher, up to 480 milliliters / 2 cups. Blend until creamy and smooth and then pour into the dutch oven. Squeeze the garlic cloves from their skin and add them to the blender pitcher, along with the rest of the roast cauliflower and as much broth as before. Blend until smooth and add to the dutch oven, along with any remaining broth leftover.
SIMMER: With all of the blended soup in the dutch oven, increase the heat to medium and add the lemon juice, black pepper, cumin and nutmeg. Bring to a gentle simmer and heat until warmed through, about 20 minutes. Taste and adjust salt, pepper & lemon juice as needed. If you like, thin with additional water or broth.
The amount of salt you may need to add will depend on the relative saltiness of the broth you use, especially as this varies wildly between brands. If your broth is on the salty side, I would wait until the roasted veggies are blended, then taste & adjust salt if needed.