Roast the Cauliflower: In a large soup pot, add cauliflower and drizzle with olive oil. Stir until coated, and cook covered, stirring frequently, over medium-high heat until cauliflower begins to brown on the outside, around 10-15 minutes. Keep an eye on them and stir frequently, you want them roasted, not burnt!
Sauté the Aromatics: Add onions, leeks, garlic, salt, and pepper. Cook covered, stirring occasionally, until onions are translucent, around 8-10 minutes.
Build the Broth: Add potatoes, vegetable broth, lemon juice, and chives. Bring to a boil over high heat, then reduce heat to medium-low and simmer, stirring occasionally, until potatoes are tender when pierced with a fork, around 15-20 minutes.
Blend: Remove from heat and let cool for 5-10 minutes. Use an immersion blender and blend until smooth, or transfer to a blender in batches. (If transferring to a blender, be sure to open a vent to let the heat escape, and cover the open vent with a towel to prevent splatter). Stir and serve with a drizzle of olive oil and more chives!
