In a large sauté pan over low-medium heat, add onions, garlic, butter, olive oil, sea salt and black pepper. Cook until onions are nice and caramelized. About 30 minutes.
While the onions are caramelizing, fill a large sauce pan with 1 inch of water. Over high heat, steam the cauliflower, whole and, covered, until fork tender – About 15 minutes. Once the cauliflower is fork tender, drain the water and remove from heat. Leave the cauliflower in the hot pan to help draw out some of the excess moisture. (Don't skip this step or your mash will turn out soupy)
Fork mash the cauliflower in the pan. Add caramelized onions, sour cream, horseradish sauce, sea salt and black pepper to the pan. Using a potato masher or hand mixer, mix all ingredients together.
Per Serving - Calories: 120 | Fat: 9.5g | Protein: 2.5g | Net Carbs: 4.5g