Warm olive oil and butter in a pot on medium heat.,Meanwhile, prepare the leeks (discard the top green portion and cut the bulbs lengthwise into four pieces, then chop into smaller sections). Add to the pot.,While leeks are sautéing, separate the cauliflower into florets that are roughly the same size. Add cauliflower to the pot.,Add chicken broth, water, ground cumin, and thyme to the pot, and increase heat to high. Once the soup starts to boil, reduce to medium-low heat and simmer until the cauliflower is tender (about 20 minutes depending on the size of the florets).,Once cauliflower is tender, remove from heat and puree using a stick blender (or normal blender), using caution as the soup is still very hot.,Serve with optional garnish immediately.