In a large pot, heat the olive oil over medium heat. Add the chopped onion and sauté for about 5 minutes until softened.
Add the minced garlic and sauté for another minute, being careful not to burn it.
Add the cauliflower florets and vegetable broth to the pot. Bring to a boil, then reduce the heat and simmer for about 20 minutes, or until the cauliflower is tender.
Remove the pot from heat and let it cool slightly. Using a blender or immersion blender, purée the soup until smooth.
Return the soup to low heat and stir in the milk. Season with salt, black pepper, and nutmeg if using. Let it warm through for about 5 minutes.
Taste and adjust seasoning if necessary. Serve hot, garnished with fresh parsley if desired.
For extra creaminess, consider adding a dollop of sour cream or Greek yogurt on top before serving.
Store any leftovers in the refrigerator for up to 3 days or freeze in an airtight container for up to a month.