In a large bowl, toss cauliflower florets with 3 tbsp melted butter and salt and pepper to taste.
Arrange cauliflower in a single layer on a large rimmed baking sheet. Roast for 25-30 minutes until the edges are golden brown, tossing the cauliflower once during baking.
Transfer cauliflower to a large pot. Add chicken broth and several sprigs of fresh thyme, then bring to a simmer for 10 minutes.
Remove pot from heat and carefully remove thyme sprigs. Then add remaining 1 tbsp butter, heavy whipping cream, and salt and pepper to taste.
Using an immersion blender or regular blender, carefully blend the soup until smooth, working in batches if necessary.
Garnish each bowl of soup with one cooked-and-crumbled strip of bacon.
Notes
For a thicker soup, use only 3 3/4 cups chicken broth.
For a thinner soup, add more chicken broth until you reach your desired consistency.
If you want this soup to be higher in fat without increasing the carb count, you can add more butter.