Amanita Muscaria mushrooms seasoned with salt and fermented in brine inspired by the Traditional Japanese technique. You can also pickle the mushrooms with vinegar for a decent, although more acidic result if you aren't experienced with fermenting. Please view my video on detoxifying muscaria to familiarize yourself with the process before attempting these.
Cut the mushrooms into pieces (see my video for reference) put in a pot of water at a ratio of 6 quarts of water to each 1 lb mushrooms
Cover the pot and bring the mushrooms to a boil, still with the lid on, then set a timer for 15 minutes.
Salting
After 15 minutes, remove the mushrooms rinse them vigorously and dry well, then put them in a glass jar or other non-reactive container placed on a scale tared to 0 in grams.
Add water to cover the mushrooms by ½ inch, weighing the water and mushrooms in grams as you pour it in. Multiply the final grams by .03 or 3%, then add that many grams of salt to the jar. A pint jar is a good place to start, for that, you can use a tablespoon of kosher salt, or roughly 13 grams. Also remember that a pint is one pound, or 448 grams, and 448 x .03 = 13.44 grams of salt. (You can use anywhere from 2-5% salt here for reference).
Add a dash of sauerkraut juice or fermented brine if you have some to speed up the process.
Fermentation
Shake the jar, weigh the mushrooms down with a clean stone or clingfilm, screw on the lid, and leave in a dish to catch any liquid at room temperature for 5 days, and up to 10, or until they taste to your liking. The mushrooms should be covered with liquid the entire time.
After that, refrigerate the mushrooms. The mushrooms will continue to age a bit in the fridge. If you want a stronger flavor, leave them out for another day or two, tasting them regularly.
They'll last for a long time if always kept completely submerged in liquid, and will continue to develop as they age.
Video
Notes
Fermenting with a vacuum bag
You can also ferment the mushrooms in a vacuum bag after boiling. To do that, dry the mushrooms well. Weigh the mushrooms in grams, multiply the number by .03, or 3%. Add that amount of salt, mix well, and vacuum seal.