Sterilize your jars and lids by boiling them for 10 minutes or running them through a hot dishwasher cycle while you prepare the mushrooms.
Clean the mushrooms: gently brush and trim the Porcini (Boletus), Saffron Milk Cap and Chanterelle; cut larger specimens into bite-sized pieces so everything is uniform.
Peel and slice the Onion into thin rings, slice the Carrot into coins or matchsticks, and lightly crush several cloves of Garlic.
Bring a large pot of water to a simmer and season with a little Salt. Blanch the mushrooms 2–4 minutes until just tender, then drain and let cool briefly — this helps remove grit and keeps them firm in the jar.
Pack the cooled mushrooms into the sterilized jars, layering in the sliced Onion, Carrot and Garlic. Distribute whole Bay Leaf, a few Allspice Berry, Black Peppercorn, a pinch of Yellow Mustard Seeds and a couple of Clove in each jar for spice and aroma.
Make the brine by combining equal parts White Vinegar and Water in a saucepan (adjust quantity to fill your jars), then add Sugar and more Salt to taste. Heat until the sugar and salt dissolve and the mixture just comes to a simmer.
Carefully pour the hot brine over the packed jars so the contents are fully submerged, leaving about 1 cm (1/4–1/2 inch) headspace. Tap the jars gently to release trapped air bubbles, wipe rims clean and seal with lids.
For quick pickles, let the jars cool to room temperature, then refrigerate and allow the flavors to develop for at least 48 hours before eating (best after 3–7 days). For shelf-stable jars, process in a boiling water bath for 10–15 minutes, then cool and store in a cool, dark place.
Store refrigerated pickles up to 4–6 weeks; if water-bath processed and sealed properly, they will keep for several months. Serve cold or at room temperature as part of antipasti, on sandwiches, or tossed into salads.
