Melt the butter, in a large pan, over medium heat. Add the onion,celery and garlic and saute for around 6 mins.
Add the cauliflower, potato and stock. Bring to a simmer, cover and cook for 20 minutes or until the potato and cauliflower is soft.
Turn the heat off, add the mustard and using a stick (immersion) blender, blitz until smooth.
Add the cheese and stir until melted.
Taste and season (do not season if serving a baby)
Notes
No stick blender?: You can use a blender or food processor. Allow the soup to cool a little and transfer to blender/processes in batches to blend. Cooking for a baby?: Use homemade or low sodium stock and reduce/omit the cheese to keep sodium levels lower. Make it Gluten Free: Make sure to use homemade stock or a stock that is gluten-free. Make it Dairy Free: This soup tastes great without the cheese, just skip it. Replace the butter with olive oil. Storage: Allow to cool, transfer to an airtight container and store in the refrigerator for up to 3 days or the freezer for up to 3 months. Nutritional information is a ROUGH guide only, calculated using an online nutrition calculator.