Preheat oven to 425 degrees. Toss cauliflower with olive oil, salt, and pepper. Divide between two trays lined with parchment paper (or greased foil). Roast until slightly browned and tender, about 35 minutes.

While cauliflower is roasting, cut bacon into ½” pieces. Heat a heavy pot over medium heat and cook bacon, stirring occasionally, until browned and crisp, 10-12 minutes. Transfer bacon to paper towels, reserving about 2 tbsp of bacon fat in the pan. 

Cook chopped fennel, onion, and garlic in bacon drippings, stirring occasionally until onion and fennel are very soft, 8-10 minutes. Add wine and cook until mostly evaporated, about 4 minutes. Add in broth, bay leaves, thyme, and roasted cauliflower. Bring to boil then reduce to simmer. Simmer uncovered for approximately 10 minutes.

Put hazelnuts in a single layer on a baking sheet. While soup is simmering, turn oven to 400 degrees and toast hazelnuts until lightly browned, approximately 10 minutes. Let cool slightly, and then coarsely chop. 

Remove soup from heat, then remove bay leaves and stir in cream. Working in batches, puree soup until very smooth. (I did this in a blender.) Return to pot and season with salt and pepper to taste. Top soup with toasted hazelnuts and bacon. Enjoy!