Cut the Napa cabbage in half lengthwise, then into quarters. Remove the core.
Cut each quarter crosswise into bite-sized pieces.
Dissolve the sea salt in 1.5 litre water in a large bowl.
Place the cabbage pieces in the salted water, making sure they're fully submerged.
Place a plate on top to weigh down the cabbage, and let it soak for 1-2 hours, tossing occasionally.
Rinse the cabbage thoroughly under cold water to remove excess salt.
Drain the cabbage in a colander for about 30 minutes to remove excess water.
In a bowl, combine the grated ginger, minced garlic, fish sauce, soy sauce, Korean red pepper flakes, and granulated sugar. Mix well to form a paste.
In a large mixing bowl, combine the drained cabbage, kimchi paste, chopped green onions, and julienned carrot.
Put on disposable gloves and massage the paste into the cabbage leaves, making sure they're well coated.
Pack the kimchi mixture tightly into clean glass jars, pressing down as you go.
Leave about 1 inch of space at the top to allow for expansion.
Loosely cover the jars and let them ferment at room temperature for 6 hours to 2 days, depending on your desired level of fermentation. Check daily and press down the kimchi if it releases any liquid.
Once the kimchi reaches your desired level of fermentation, seal the jars and refrigerate to slow down the fermentation process.
Kimchi is best after a few days of refrigeration but can be consumed immediately.
Enjoy your homemade kimchi as a side dish, in stir-fries, soups, or any way you like!