Put cauliflower and vegetables on a parchment lined baking tray (you may need two) and drizzle with 1 - 2 tbsp of olive oil - toss to coat then sprinkle with sea salt
Bake at 200 - 210 C for approximately 35 minutes, tossing half way
When the veggies are nearly cooked, heat 1 tbsp of olive oil in a soup pot on medium heat and add chopped onions. Saute, stirring occasionally for 5 - 7 minutes or until softened and translucent
Add minced garlic and chilli and cook for 30 seconds stirring constantly
Reserve 4 of the prettiest florets of cauliflower (if you want to be fancy) and add the rest of the roasted veggies to the pot with the broth. Increase heat to medium - high until simmering, then reduce to low so that the pot simmers for about 20 minutes - so that the flavours meld.
Let the soup stand for a few minutes to cool, and then add to a blender jug, and blend on the hot setting. Be careful to not overfill the blender or hot soup will escape and potentially burn you.
Once blended, add the butter and lemon juice and blend again.
Serve with a reserved floret and some chopped parsley for garnish.