In a large pot over high heat, melt the butter and add the oil, garlic, red pepper flakes and onions. Cook for 2-3 minutes until the onions are soft. Lower the heat to medium and add the cauliflower. cook for about 5 minutes until the cauliflower is softer then add the vegetable broth. Bring to boil and simmer for 30 minutes.
Turn off the heat and either use a hand blender or a regular one. Blend until pureed and without any lumps; you want a velvety texture.
Season with salt and pepper, sprinkle with cilantro or fresh parsley and serve.