Preheat your oven to 400° and line a rimmed metal baking sheet with parchment.
Add the cauliflower to the prepared pan and toss with olive oil and a couple pinches of salt.
Roast for 20-25 minutes. Let cool for a few minutes and then toss in a blender with the milk.
Meanwhile in a large Dutch oven, cook bacon on medium-low heat until crispy, turning often. Remove the bacon to a paper towel lined plate and set off to the side.
To the bacon fat in the pan, add in the yellow onion, white and light green onion parts and garlic. Stir and cook for 5 to 8 minutes or until softened.
Next add in 1 pound both peeled and chopped Yukon gold and russet potatoes, 6 sprigs fresh thyme and 1 bay leaf. Pour in 4 cups low sodium chicken broth.
Cover and bring to a boil. Reduce the heat and simmer for 15-20 minutes (more or less depending on the size of the potatoes).
Once the potatoes are cooked through, use a immersion blender and puree soup until desired consistency.
Lastly add the cauliflower puree, greek yogurt and season with 2 teaspoons kosher salt and lots of freshly ground black pepper (or to taste). Stir and warm until heated throughout.
Ladle the soup into bowls and top them with chopped crispy bacon pieces, sliced green onions and freshly ground black pepper.
Serve with torn crusty bread.
