Line a large saucepan or Dutch oven with a steamer basket. Fill the pot with 1 inch of water and bring to a low boil.
Add the cauliflower florets and cover the pot, allowing them to steam for 15-20 minutes or until nearly falling apart.
Carefully remove the steamer basket and transfer the cauliflower to a large mixing bowl. Add the butter, Greek yogurt (or sour cream), Kosher salt and black pepper. Mash with a potato masher. If you want smoother, whipped cauliflower, use a ricer or the food processor.
Cauliflower can be watery, heat on low, stirring continuously to evaporate remaining water, if needed.
Top your cauliflower mashed potatoes with ground black pepper and chives.
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