Warm oil in a large saucepan over medium heat. Add garlic and anchovies; sauté for about 1 minute, until garlic is fragrant and anchovies melt. Place cauliflower on top; cook for 2 to 3 minutes, turning a few times to coat with garlic oil. Pour sauce over (sauce won’t completely cover cauliflower). Stir in olives, capers and crushed red pepper flakes, if using. Season with pepper. Bring to a boil, then reduce heat to a simmer.
Cover pan and cook until cauliflower is very tender, about 40 to 50 minutes (a knife inserted into cauliflower should go in easily), stirring once or twice and turning cauliflower as it cooks.
Cut cauliflower into smaller pieces and divide among 4 plates. Top with sauce; drizzle with olive oil. Top with parmesan, if using, and parsley. Serve hot.