Surprising harvest

Guess what this is? I took this picture today. It is my Globe Artichoke plant, grown from seed this year, and it is producing a fruit...at this time of year!We had a deep frost this morning....what is it thinking of?

I went to the plot today to dig spuds and saw it....I'm amazed.

I expect someone will read this and tell me it is quite usual....I do hope so.
Will I be able to harvest this and eat it? If so, how long should I leave it before I pick it?

Tomorrow I am going to the plot to plant my shallots. I have to do it this week rather than leaving it til next (supposed to be the shortest day according to my book) because I have a date for my op next Monday....hooray!