To a large saucepan, add 2 tablespoons oil over medium heat. Add the fennel and onion. Cook, stirring until the onions start to soften, about 8-10 minutes. Add the garlic, salt, pepper and rosemary then cook for 1 minute. Add the cauliflower and chicken stock and bring to a simmer for 10 minutes.
Turn off the heat and use an immersion blender or transfer to a blender in batches and blend until smooth. If it’s too thick, add a little stock or water.
Serve topped with chopped bacon.
Make the Parmesan crisp/frico:
To make the Parmesan crisp/frico: Heat a non-stick frying pan over medium heat. Sprinkle 1 tablespoon of grated Parmesan cheese into the pan. Let it cook for 1–2 minutes until the cheese melts and the edges turn golden and lacy.
Use a thin spatula to carefully lift the crisp from the pan. Transfer to a plate or paper towel to cool and harden.