Place the cabbage in a large bowl and toss with 4 cups of water and the salt. Let sit for 2 hours, tossing the cabbage every 30 minutes. Drain, rinse with cold water and gently pat dry to remove any excess moisture.
Add the rice flour and 2 cups of water to a small saucepan over high heat. Bring to a boil, and then reduce the heat to medium-low. Cook for 20 minutes, whisking constantly, until the liquid is thickened to a ribbon-like consistency and you can see the bottom of the pan while whisking. Set aside to cool.
Combine the fish sauce, sugar, salted shrimp, garlic, ginger, onion and apple pear in a food processor and pulse until smooth. Pour the mixture into a large bowl and then mix in the sweet rice paste and gochugaru until smooth. This will be the kimchi sauce base.
Place the leeks, daikon and scallions in a large bowl and mix with the kimchi sauce. Gently add the cabbage and carefully toss all of the ingredients together until fully incorporated, making sure not to bruise the cabbage. Tightly pack the kimchi into jars or containers with tightly fitting lids, or cover tightly with plastic, making sure it is not exposed to the air. Allow the kimchi to sit at room temperature for at least 2 days, or longer if you desire a stronger flavor. Refrigerate until ready to use.