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1
Place the dried gosari in a large bowl and cover generously with cold water, then soak for a minimum of 4 hours — cold water draws the bitterness and any residual astringency out of the fern gradually without cooking it soft before heat is applied. Drain, cover again with fresh cold water, and soak overnight, a minimum of 12 hours further, for a total soaking time of no less than 24 hours across at least two changes of water, replacing the water so that the bitter compounds pulled from the fern are discarded and not reabsorbed. The fully soaked strands will have darkened uniformly and swollen to a supple, pliant rope; any strand still rigid at its centre has not soaked long enough.
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2
Drain and rinse the soaked gosari under cold running water, then bring a pot of water to a full boil and blanch the gosari for 2–3 minutes — the fierce heat of a rolling boil drives out the last of the bitterness that soaking alone cannot reach, and it sets the fern's texture so the strands stay cohesive through the subsequent stir-fry. Drain immediately so the residual heat does not carry on cooking and soften the strands past the point of no return. The strands should yield cleanly when pressed between finger and thumb — no woody resistance — and the colour should be a deep, uniform brown-black throughout.
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3
Cut the blanched gosari into lengths suited to the intended use — longer for bibimbap, shorter for standalone banchan — so that every strand sits well against whatever it accompanies and is easy to eat in a single motion. Heat a wok or heavy skillet over medium heat and add the sesame oil; when the oil shimmers and carries a faint toasted fragrance, add the minced garlic and stir briefly until fragrant but not coloured, since garlic that colours at this stage will turn sharp and acrid once the soy sauce hits the pan.
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4
Add the gosari to the pan and turn continuously to coat every strand in the sesame oil before the ganjang goes in, because strands left dry will absorb the soy sauce unevenly and some will taste flat while others taste over-salted. Add the ganjang and continue to stir-fry over medium heat, turning without pause, until the seasoning is fully absorbed and each strand carries a glossy, dark, even sheen with no pooled liquid remaining in the pan.
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5
Transfer to a serving dish. Each strand should be uniformly dark, glossy, and tender throughout its length — taste to confirm: the flavour should be deeply savoury and woodsy with no trace of bitterness or acrid note.