This is the recipe from the food pairing & whisky tasting. It’s originally a Jamie Oliver recipe that I’ve adapted. On the evening we had large jars but if you can you should use smaller ones because once a jar's been opened it will only last for a week in the fridge. It makes about 2 litres

pickling liquid:
1 litre cider or white wine vinegar
1 litre water
2 tablespoons sea salt

pickling marinade:
500 ml extra virgin olive oil 5 cloves of garlic, peeled and sliced
1 fresh chilli, deseeded and chopped

1 kg mixed mushrooms (cleaned) like chestnut, chanterelle shitake, enokitake - anything you like really just don’t use regular white mushrooms
a few sprigs of fresh thyme, rosemary and sage

Make sure you sterilize your jars before you start. Bring all the pickling liquid ingredients to the boil in a large pan. Slice your vegetables any way you like, I normally use a mandolin on a thick setting. Like maybe 5mm to 10mm. You need to do this so as the flavours and pickling liquid will penetrate enough. Smaller pieces, like baby mushrooms or really small onions, can be left whole. 
Put the pickling marinade ingredients into a large bowl with the herbs and mix. 
Put the sliced vegetables in the boiling pickling liquid and leave for around 3 minute. Push them down to ensure they are all immersed. Lift the pieces out with a slotted spoon and place them into your bowl of pickling marinade and toss them together.
After 3minutes, put the hot vegetables and pickling marinade into your sterilized jars. Make sure you fill them to the top. Cover everything completely with the marinade and put the lids on tightly. 
Put the jars to one side until they're cool. Clean the outside of jars, attach sticky labels and write the date and the contents on them. Store the jars somewhere cool and dark - it's best to leave them for about two weeks before opening so the veg really gets to marinate well, but three days later is also fine. The longer you wait the better everything tastes.

If you want to make pickled onions & fennel then use the following instead of mushrooms:

500 g fennel bulbs and their tops
500 g of small mixed onions & shallots and 4 bay leaves