Cut the cabbage lengthwise into quarters. The best way to do this is by cutting the stem end in half about 3 inches from the end then slowly pulling apart the two pieces.
In a large bowl, dissolve 1/2 cup of salt in 5 cups of water. Plunge each cabbage quarter in the saltwater one at a time, shake off excess water back into the bowl and then transfer to another bowl. Reserve salt water for later.
Using the other half cup of salt and starting from the outermost leaf, sprinkle salt over the thick white part of each leaf. Pour the remaining salt water from the first bowl over the cabbage. Set aside for about 8 hours, rotating the bottom ones to the top every 2 or 3 hours. Wash thoroughly 3 times with fresh water, especially between the white parts of the leaves. Drain well.
Meanwhile, make the rice flour paste and cool. Prepare the other seasoning ingredients. Mix all ingredients well, including the rice paste. Set aside while preparing the other ingredients.
Cut the radish into match sticks. Cut scallions into 1 inch long pieces. Transfer to a large bowl and combine with seasoning mix. Mix well. Let sit for an hour to let the flavors comes together.
Cut the tough stem part from each cabbage quarter leaving enough to hold the leaves together. Place one cabbage quarter in the bowl with the radish mix. Spread the radish mix over each leaf using 2 tablespoons for the larger leaves and dividing it up evenly among the leaves. Fold the leafy part of the cabbage over toward the steam and wrap with the outermost leaf. Place it, cut side up, in a jar. Repeat with remaining cabbage leaves. Press down hard to remove air pockets. Rinse the bowl that contained the seasoning mix with 1/2 cup of water and pour over the kimchi. Leave it out at room temperature for 2 days to ripen. Store in refrigerator for about 2 weeks to develop it's flavor before eating.