1. Place a medium saucepan over medium heat and add the butter or olive oil. Add the onion and fry until fragrant and translucent but not browned, about 3 minutes. Add the cauliflower and stock and bring to a simmer. Simmer for about 10 minutes, until the cauliflower has softened, then transfer to a blender and blend to a smooth puree. Add the yoghurt, season with salt to taste and serve. 

Adam's tip: A high-speed blender is a very useful tool in the kitchen, particularly for soups. It will give you  a silkier texture than normal blenders will, and you won't need to bother with a strainer.

Also try: Adam Liaw's salted honey and tahini shortbread