This is a fabulous recipe that I found in my grandma’s journal. When I first tasted it I couldn’t believe how simple yet sophisticated it is; how much it altered my view of what mushrooms can do; and how little it associated with the grotesque kind of British party food pictured in vintage cookery books from the 1950s and 60s.
You needn’t bother with any canning or sterilising to make this pickle, although you do need to start it ahead of time to let the mushroom slices marinate in vinegar solution. This effectively ‘cooks’ the mushrooms through denaturation – in much the same way citrus juice does raw fish in a ceviche. The result is a mushroom that retains both its freshness and its firmness, with a subtle earthy flavour that is enriched with good olive oil and Dijon mustard and brightened with the acidity of the pickling liquor and fresh herbs - go right ahead and use whatever you have to hand.
The dish works perfectly with grilled or barbecued oily fish such as mackerel, and makes an unusual addition to a summer spread of salads. To my mind it’s the perfect way to display how clever you are at cooking without really doing any cooking at all.