Add the cabbage and coarse salt to a large bowl. Mix by hand until all the cabbage leaves are completely coated in salt. Let stand at room temperature for 3 hours.

Check if the cabbage leaves are soft after 3 hours have passed. If they are still crisp, let stand for another 30 minutes.

Rinse the cabbage thoroughly in a colander under running water to remove the excess salt. Let it drain for at least 1 hour. Once dry, transfer the cabbage to a large bowl.

Add the cold water, mushrooms, and kombu to a pot and bring to a boil over high heat. As soon as the water begins to bubble, remove the kombu. Turn off the heat and let the mushrooms steep for 10 minutes. Remove the mushrooms and let the broth cool completely.

Once the broth has cooled, add the rice flour and mix well to break up any lumps. Return to a boil, whisking continuously until the mixture thickens, 2 to 3 minutes. Transfer to a bowl and add the garlic, ginger, fine salt, applesauce, and gochugaru. Puree the mixture with an immersion or stand blender.

Add the carrot, daikon, and scallion to the sauce and stir to combine. Pour the mixture into the bowl of cabbage, add the sesame seeds, and mix by hand. (Be careful, it’s spicy! Wear gloves to protect your hands from the gochugaru.)

Transfer to an airtight container and ferment for 5 days at room temperature. Once fermented (the kimchi should smell slightly sour), move the airtight container to the refrigerator.