Trim the cauliflower to its florets and put them in a pan of water. Bring to the boil then simmer until tender, for about ten minutes.
Meanwhile, finely chop the spring onion and mince a garlic clove, if used.
Heat the oil in a medium pan over medium high heat, then add onions and sauté for about 5 minutes. Add the garlic and chilli, if used, and stir for 30 seconds.
Add the spinach, toss, cover and turn down the heat.
After a minute of steaming turn off the heat.
Drain the cauliflower, retaining a cup of the cooking water.
Mash the cauliflower with the butter, using a potato masher or stick-blender, until you get a textured finish (not a purée).
Add the spinach mixture, salt & pepper, then combine.
If the mash is too thick, add a few drops of the cooking water.
Serve immediately or divide it into portions, and adjust those according to your menu, diets, allergies etc.