You can buy this commercially but making your own is just way more fun.
Use Maldon sea salt flake, as they have this natural dampness which acts as a natural conduit for this infusion.
Dehydrated mushrooms are readily available, so pick a favourite or blend of, and crush/whizz/slice into oblivion into a fresh pack of damp sea salt. The longer you leave it, the better but I'm impatient so I toasted half the mix in a pan, blitzed to dust then added back to the jar. Keep tinkering until you hit that umami sweet spot. The beauty lies in being able to add all that compliments a mushroom; thyme, lemon, garlic, pepper, chilli- even sugar.
Suddenly any dish is elevated and enhanced without essentially altering the recipe.