Preheat oven to 400F.
Toss cauliflower, leek, garlic and olive oil in large bowl before spreading out on large baking sheet.
Bake 25-30 minutes, tossing at the 15 minute mark. Add leaves for the last 10 minutes if using.
Combine all sauce ingredients except pasta water in blender or food processor until smooth. Check for desired creaminess. Add small amounts of pasta water if you like it thinner.
Add roasted veggies,and sauce to pot. Combine on low temp until heated through.
Sprinkle with parmesan if desired. Serve immediately.