Bring a large pot of salted water to the boil.

While waiting, peel the potatoes, carrots and parsnip.  Chop into same-sized pieces.

Boil the vegetable cubes for approximately 10 minutes; until you can stick a fork through them.

Add the spinach and cook for a further 2 minutes.

Drain the vegetables into a sieve.

Add the butter and milk to the pot. Put on the heat to warm up a little.

Add the vegetables and stir vigorously to start to break them up and to melt the butter entirely.

Scrape the mixture into a blender.  Add the anchovies, if using.

Blend until the consistency is very smooth.  Add more milk if necessary.

Leave to cool until tepid before eating.

NOTE:  this can be used as baby food if you omit the salt and anchovies.