Preheat the oven to 180 degrees Celsius (FAN), 350 Fahrenheit FAN, gas 6 or static oven 200 degrees Celsius or 400 Fahrenheit.
Cut the cauliflower heads in bite size florets and wash them. Allow them to either rest in the strainer to drain the excess water or use a clean teatowel to speed up the process.
Toss the florets in a bowl and season with salt and ground black pepper, and three tablespoons of olive oil. Ensure all the pieces are evenly coated, then spread them on a baking tray covered with parchment paper.
Peel 3 or 4 garlic cloves and place them in a piece of aluminum foil with a couple of teaspoons of olive oil. Close the aluminum foil around the cloves, so that it protects the garlic from overcooking. Place it on the same baking sheet as the cauliflower.
Place the tray on the middle shelf in the oven and roast the cauliflower and garlic for 20 minutes, then turn the cauliflower, and roast for another 10 minutes. You can roast the vegetables for a little longer if you want a stronger roasted cauliflower taste.
OPTIONAL: Set aside a handful of the smaller roasted florets to add them on top of the soup before serving.
On medium heat, heat up a tablespoon of olive oil in a saucepan or dutch oven, and once warm, add the sliced onions to it. Sautee the onion with a pinch of salt until it becomes soft and translucent.
Add the roasted garlic and cauliflower to the saucepan and add just enough vegetable stock to cover the vegetables. For 2 lbs [900g] of cauliflower florets, you will require about 4 cups of veg stock.
Warm the soup up and allow it to simmer for 10 minutes, then allow it to slightly cool down for 5-10 minutes.
Finally, add the soup in bathes to the blender and blend it with the butter. The soup will have an airy and creamy texture.
Once all the soup has been blended, mix it with the freshly grated nutmeg and lemon juice, and warm it up again.
Taste for seasoning and adjust if necessary by adding more salt and pepper to taste.
Serve this cozy soup with a few roasted cauliflower florets on top. Garnish with a few chili flakes, thin slices of green onion, or some homemade croutons. Enjoy!