Cut the limes into four wedges. Spread a layer of miso at the bottom of a jar, then press in a layer of limes. Spread more miso on top, then press in more limes — you want to eliminate any air pockets — and repeat until you get close to the top, covering the last layer with miso. Sprinkle on the salt. Push in a fermentation weight, lid the jar loosely so gases can escape, and put it somewhere cool and dark for a month. At this point you can use both the miso-flavored limes and the lime-flavored miso; it’s hard to say which is more delicious! If you keep the fruit buried in the miso, they’ll last happily for several months in the fridge.