2-inch-high steamer rack
Two 9-inch round cake pans
Pot large enough to hold both the rack and the cake pan when covered
1. Make the Batter: Combine the rice flour, wheat starch, salt, and pepper in a large bowl and set aside. Drain and finely chop the shrimp.
2. Peel the daikon and grate it through the small holes of your grater onto a kitchen towel. Bring together the ends of the cloth and twist to squeeze out as much of the liquid as you can into the bowl. Measure out the collected juices and add enough water to the juice to make 3½ cups.
3. Pour the daikon liquid into a medium pot. Add the grated daikon and bring to a boil over high heat. Cover, reduce the heat to low, and simmer for 5 minutes. Mix in the sausage, scallions, and chopped shrimp, cover, and cook for 5 minutes longer. Remove from the heat. Slowly add the rice flour mixture and whisk continuously until free of most large lumps. The batter will be thick and sticky and a little lumpy.
4. Steam the Dumplings: Place the steamer rack in the pot, add 1½ inches of water to the pot, and bring to a boil over high heat.
5. Brush both cake pans with a little oil and divide the batter between the 2 pans. Dip a spoon into cool water and use the back of the spoon to smooth out the surface of the batter.
6. Carefully place one of the filled pans on the steamer rack, cover, and steam for 40 minutes. The other filled pan should be covered and left sitting at room temperature while the first one cooks, or it can be cooked simultaneously in another pot.
7. Remove the pot from the heat. Carefully lift the pan out of the pot, place it on a folded kitchen towel, and allow the luo bo gao to cool to room temperature. Cook the other filled cake pan.
8. Unmold the luo bo gao and gently turn it onto a cutting board. Cut each dumpling into 8 equal slices. (Do not slice the luo bo gao if you are planning on serving it later. They can be refrigerated, tightly wrapped, for up to 3 days. Slice and fry just before serving.)
9. When ready to serve, coat a large skillet with oil and heat over medium heat. Carefully place the slices of luo bo gao in the pan and cook until their bottoms are crispy and golden brown, about 4 minutes. Turn them over to brown the other sides. Serve with a side of oyster sauce or hot sauce.