Preheat: Oven to 180°C (350°F).
Roast: Toss bite-sized cauliflower florets with 2 tbsp olive oil, salt, and pepper. Roast for 20 minutes, or until slightly charred.
Clean: Wash leeks, thinly slice, then submerge in cold water to remove grit.
Sauté: Heat remaining oil in stockpot, add leeks, salt, pepper, and cook until softened.
Add: Cubed potatoes (skin on) and cook for a few minutes.
Simmer: Prepare 2.5 litres vegetable stock, add to pot along with torn parsley (reserve some for garnish).
Combine: Once cauliflower is roasted, add it to the pot. Simmer for at least an hour, stirring occasionally.
Blend: Puree soup with an immersion blender until desired consistency is reached.
Season: Taste and adjust salt and pepper. Serve with crusty bread, parsley, olive oil, and optional vegan parmesan.