Preheat oven to 400 degrees. Place a rimmed baking sheet in the oven while it preheats.

Meanwhile, process the cauliflower heads, discarding the leaves and core and chopping it into chunks. (Learn how to in the post above.)

Toss the cauliflower in a large bowl with 6 tablespoon of the olive oil and sprinkle with salt and pepper. Carefully pour onto the hot baking sheet and roast in preheated oven for 60 minutes, stirring halfway through. Remove cauliflower when it is golden brown and fork tender.

Place a large Dutch oven over medium heat and add the remaining 2 tablespoon olive oil. Stir in the onion and cook until it begins to soften, about three minutes. Stir in the garlic and cook until fragrant, about another minute. Season with salt, to taste.

Add the roasted cauliflower and vegetable stock to the Dutch oven. Increase heat to high and bring the soup to a simmer. Add a pinch of red pepper flakes. Taste, and adjust seasoning if necessary.

Remove soup from heat and puree. Do this either with an immersion blender directly in the pot or by carefully pureeing it in batches in a powerful kitchen blender.

Stir in the cream. Serve with another pinch of red pepper flakes and a drizzle of garlic-infused olive oil if desired.