The riddle
What Do You Call a Fake Noodle?
Impostor, said fast
An impostor is someone who pretends to be a person he or she is not. Merriam-Webster gives the American pronunciation of impostor as im-PAH-ster, and pasta as PAH-stuh. Said aloud in American English, the two words match except for the very end, where impostor has an r sound and pasta has a plain uh. That is about as near as a pun gets. In British English pasta usually has a flat a, so the match is looser there.
Noodle, pasta and what is fake
Merriam-Webster defines a noodle as a food paste made of flour, eggs and water, dried in strips, and pasta is the Italian word for paste. A noodle that only pretends to be one is an impostor, and the word is built by joining the start of impostor to the end of pasta. It is a made-up word, so the pun lives in the sound alone.
Building your own
The recipe is to pick a word for a fake, such as impostor, and look for a food word that overlaps with it. A group can try other food words with other fakes, but few hold together as well, and most need a longer pause before the answer.
Telling it at the table
Ask the question, wait for guesses such as "a pretend noodle", and then give the answer, leaning on the middle of the word. The groan is usually quick, so no explanation is needed unless a young listener does not know the word impostor.