Gather ingredients: napa cabbage, kosher salt, Korean radish (optional), garlic, ginger, gochugaru (Korean chili flakes), fish sauce or salted shrimp (optional), sugar (optional), scallions, carrots (optional)
Prepare brine: dissolve kosher salt in water (use enough to fully submerge cabbage)
Cut napa cabbage into bite-size pieces
Soak cabbage in brine 6–12 hours (turn pieces once if needed)
Rinse cabbage thoroughly under cold water
Drain well and squeeze lightly to remove excess water
Make seasoning paste: blend or mash garlic and ginger
Mix gochugaru with the garlic-ginger mixture
Add fish sauce or salted shrimp and sugar (optional), adjusting to taste
Grate or julienne radish and carrots (optional)
Chop scallions
Combine vegetables with seasoning paste until evenly coated
Pack into a clean jar, pressing firmly to remove air pockets
Leave 2–3 cm headspace at the top
Ferment at room temperature 1–5 days until bubbles and sour aroma develop
Check daily and press down if vegetables rise
When fermented to your taste, refrigerate to slow fermentation
Eat after at least 1–2 days in the refrigerator
Store refrigerated and use within several weeks