I was once given a jar of these as a gift from an Italian friend. I loved them so much I had to know the recipe. They come from a lovely lady, Maria Falvo, who learnt this method in her home town of Calabria where there was an abundance of wild porcini mushrooms.
300g pine mushrooms (or portabello or shitake, cleaned and destemmed)
1 cup white wine vinegar
3 tbsp salt
3 cups water
about 2 cups olive oil (I like to use a mixture of half olive and half extra virgin)
2 cloves garlic
1 sprig rosemary
Bring the vinegar, salt and water to the boil in a tall narrow pot (you can use a bigger pot but you will probably have to double the amounts of pickling solution). In batches, cook the whole mushrooms for a few minutes until tender when pierced with a skewer. Remove with a slotted spoon to a rack and continue until all the mushrooms are cooked.
Be careful not to overcook the mushrooms as they absorb water quickly and can become soggy.
Now gently press out excess liquid with a tea towel and cut into thin slices. Taste to see if they need any extra salt.
Place in a sterilised jar with slivers of garlic, the rosemary and enough oil to cover.
They keep well in the fridge for a few weeks.