Mrs Beeton's cookbook was the obvious place to look, to find something as old fashioned as a pickled walnuts recipe. And sure enough, although the index on the (updated) reprint is lousy, there it was. A search online for recipes didn't have much to offer in variation other than specifying a few less days of pickling in brine, so we decided to try Mrs. B's. 

Walnut shells I've learned, start growing inside the soft outer case from the end opposite to the stalk. So, if you are trying to see if they're soft and ok for pickling, you prick that end with a fork. Then you need to prick them all over to absorb the salty brine but we didn't get that far. These had a hard shell already and although the inside is still soft and mashed when I broke one open, they would be too tough to pickle. 

The process involves soaking in the salt water for days, leaving the nuts in the sun to blacken, and then preserving in vinegar. Maybe I'll try some next year because there are always some on the ground, as they fall off easily.

So, with preserving in mind and time at hand, I switched to the onions. I peeled the smallest ones, made up a mix of warm vinegar with a packet of pickling spices, and let that steep for a couple of hours.  It was then strained through some kitchen paper towel, and poured onto the onions. I didn't have enough brown vinegar, so I mixed in a bottle of rice wine vinegar that's been waiting for a sushi session. You need to leave the onions pickle for a month or so. ( I drained, strained and boiled up the vinegar with some sugar to try and cut the bitterness a month later. They're now much milder and being eaten fast.)