Bring water in a large pot up to ¾ full to a boil.
Trim off any brown spots on the cauliflower. The easiest way to chop cauliflower into florets is by cutting a whole head of cauliflower into quarters first, then slicing the stem part and breaking away the florets.
Break up the florets, put them in a bowl, and give them a rinse.
Once the water has boiled, carefully add the florets to the pot. You may need to cut the florets into medium-chunky pieces to fit in the pot. Boil until they are fork tender.
Drain the cauliflower and put it back into the pot. Use an electric stick blender to mash it up, or put the florets in a food processor and blend to break it down into a mash.
Add whipping cream, butter, salt and white pepper and mash until smooth and fluffy. You can add herbs or any other flavourings you like.
Transfer to a serving bowl, and add a dollop of butter and tarragon.