Heat olive oil in a large pot over medium heat. Add the onion and garlic, and sauté until fragrant and translucent.

Add the cauliflower and broccoli to the pot, and cook for 5 minutes, stirring occasionally.

Pour in the vegetable broth and bring to a boil. Reduce heat to low, cover, and simmer for 20 minutes, or until the vegetables are tender.

Using an immersion blender or a regular blender, puree the soup until smooth. If using a regular blender, blend in batches and be careful not to overfill the blender.

Return the soup to the pot and stir in the heavy cream. Season with salt and pepper to taste.

Simmer for an additional 10 minutes, stirring occasionally.

Serve hot, garnished with fresh parsley.