Preheat the oven to 400 degrees F. Cut the cauliflower into florets and steam for 7-8 minutes.
Drain the cauliflower in a colander and add to a food processor (if you do not have a food processor you can use a potato masher). Add the milk or heavy whipping cream to the food processor and puree for 2-3 minutes until smooth, it is ok if there are a few lumps in the cauliflower puree. The less lumps, the fluffier this bake will be.
Add the pureed cauliflower to a large bowl and mix in the sour cream, crumbled bacon, chives, shredded cheese, garlic, salt, and pepper. Mix until combined
Add the cauliflower mixture to a 8 x 8 inch casserole or baking dish. Optional, top with extra shredded cheese and crumbled bacon. Bake for 15-20 minutes until cheese is melted and bubbly. Garnish with chives and enjoy!