Starchy ingredient of Xmas pudding (4)

I believe the answer is:

spud

I'm a little stuck... Click here to teach me about this clue!

Here is my best explanation:

'starchy ingredient' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I can't see?

'of xmas pudding' is the wordplay.
'of' indicates a hidden word.
'SPUD' is hidden in the letters of 'xmas pudding'.

Can you help me to learn more?