Prepare the vegetables: Cut the cabbage in half lengthwise, remove the core, and slice into 1 1/2-inch pieces. Trim the green onions and cut into 2-inch pieces.

Salt the cabbage: Place the cabbage and green onions in a bowl, sprinkle with salt, and toss to combine. Cover and let sit at room temperature until the cabbage wilts (about 1-2 hours).

Make the rice thickener: Combine rice flour and water in a saucepan and cook over medium heat, stirring constantly, until thick. Let cool.

Make the chili paste: Mix gochugaru, garlic, ginger, fish sauce, sugar, water, and 2 tablespoons of the cooled rice thickener.

Combine ingredients: Rinse the wilted cabbage, massage the chili paste into it, and pack into a 1-quart jar. Press down to ensure the brine covers the cabbage.

Ferment: Seal the jar and place in the refrigerator. "Burp" it daily by pressing down on the cabbage to release trapped air.