Place the sliced napa cabbage strips in a large bowl.

Sprinkle the cabbage with coarse salt and pour in the water. Toss well to coat and let sit for at least 1 hour and 30 minutes, stirring every 30 minutes to ensure even brining.

Rinse the cabbage three times under running water to remove excess salt, then drain. Squeeze the cabbage to remove liquid, but leave a small amount of moisture if you prefer a juicier finished kimchi.

Combine the water and glutinous rice flour in a small saucepan over medium-low heat. Whisk continuously until the mixture thickens into a very thick, translucent paste, then remove from heat and let cool for a few minutes.

Place the cooled flour paste, sugar, garlic, ginger, gochugaru, and onion in a blender. Process until the mixture is smooth and the aromatics are fully incorporated.

Add the julienned carrot and sliced scallions to the drained cabbage. Pour in the kimchi paste and toss until every piece of cabbage is thoroughly coated.

Pack the mixture into clean jars, pressing down firmly with a spoon to remove air pockets. Leave the jars about three-quarters full, as the kimchi will expand and release gas as it ferments.

Seal the jars and leave them at room temperature for 24 to 48 hours. You will know it is working when you see small bubbles forming in the jar and the aroma becomes pleasantly sour.

Transfer the jars to the refrigerator once you are happy with the level of fermentation. Serve chilled as a side dish or use as a base for stews and stir-fries.