Add the grated daikon radish and water to a wok or large pan and bring to a simmer. Simmer for about 10 minutes, stirring occasionally so the white radish does not brown. The daikon radish will produce liquid, some of which will evaporate. 

Scoop the cooked daikon radish into a large mixing bowl to cool. Pour any remaining liquid in the wok into a measuring cup and add water until you have a total of 250ml of liquid. Add it to the mixing bowl with the cooked daikon radish. 

Clean your wok or pan and place it over medium heat. Add cooking oil. Add the dried shrimp, shiitake mushrooms and cook for about 5 minutes. Stir in the chopped scallion and remove from the heat to cool.

Add rice flour, cornstarch, salt, sugar, and white pepper to the mixing bowl with the daikon radish and cooking liquid. Mix well until the dry ingredients are well-incorporated. 

Add in the cooked shrimp, mushrooms, and be sure to scrape the oil from the pan into the batter. If you like your radish cake soft, you can add another 60ml or more of boiling water to the batter. If you feel the batter is too thin, return it to the wok on low heat to thicken the batter while stirring. Mix well and let sit for 15 minutes.

Give the batter a final stir and pour it into a well-oiled loaf pan. Place the pan into a steamer with plenty of water and steam over medium-high heat for 50 minutes.

Remove the pan from the steamer and let your radish cake set for about 30 minutes. Once cool, loosen the sides with a spatula and turn it out onto a cutting board. It should come out quite easily.