To prepare the cauliflower, pull and cut off the green leaves. Cut the head in half from the top to the bottom. Cut out the core, and then cut the top into smaller pieces leaving some stem attached. You want bite-sized florets that look like little trees of cauliflower.
Toss the cauliflower with olive oil and salt and place in the oven. Roast the cauliflower for 20 minutes.
While the cauliflower is roasting, puree the capers, garlic, vinegar, and parsley in a food processor. While the machine is running, drizzle in 1/4 cup olive oil. Taste and season with salt, if needed.
Toss the roasted cauliflower with the vinaigrette and sprinkle with the raisins.