In a large bowl, whisk the glutinous rice flour, ground ginger, and salt together. Set the bowl aside.
Snap the slabs of brown sugar into smaller pieces and place them into a saucepan. Add the water to the saucepan, cover it with a lid, and bring the water to boil. Keep the water boiling until the brown sugar slabs have completely dissolved. Some of the brown sugar slab will get stuck to the bottom of the saucepan, so make sure to stir occasionally. If you are using regular brown sugar, this should only take a few minutes.
Once the sugar slabs dissolve, turn off the heat. Then, pour in the coconut milk, oil, and kansui into the saucepan and stir. Let the liquids cool for 5 to 10 minutes
Gradually stir the liquid into the bowl with the flours. I usually add about 1/3 of hot liquid at a time and stir the batter before adding more liquid.
Stir the batter for several minutes. The batter will feel stiff at the beginning, but should loosen up after about a minute of stirring. Stir until there are a few small lumps of flour in the batter.
Place a fine mesh strainer over another bowl and pour the batter through the mesh. This will help to get rid of any lumps that remain in the batter.
Lightly grease a 9-inch cake pan or any circular 9-inch metal pan (see note 4).
Pour the batter into the greased pan. Hold onto the cake pan and tap it gently on the counter several times to get rid of any tiny air bubbles.
Then, cover the cake pan with foil. It’s not necessary to cover the pan with foil, but it helps to ensure that the nian gao will cook more smoothly on the top.
Place a steaming rack inside a large wok (at least 14” wide). Then, fill the wok with water until there’s about a 1/2-inch gap between the water line and the top of the steaming rack. (See note 5 about overfilling/underfilling the wok with water.)
Cover the wok with a lid and bring the water to boil.
Once the water has boiled, carefully place the cake onto the steaming rack and cover the wok with the lid. Reduce the heat to medium. Steam the cake over medium heat for 50 minutes to 1 hour if you are using a thicker cake pan, about 45 to 50 minutes if you are using a thinner pan. Halfway through the steaming process, add more water to the wok as water evaporates over time.
To test to see if the cake is done, stick a chopstick into the center of the nian gao and dig out some of the cake. The cake should look brown and slightly translucent. (See note 6) Insert a jujube into the center of the cake for decoration and to cover the hole made with the chopstick.
Once the nian gao is fully cooked, let it cool on the counter overnight. I usually cover the cake (after it's cooled) with foil overnight. Assuming that your house isn’t hot and humid, you can leave the nian gao on the counter for 1 to 3 days. I usually store the nian gao in my fridge after 3 days.
Pan Frying Nian Gao: The best way to enjoy the nian gao is to pan fry it. Once the nian gao hardens overnight, it is easier to slice. Cut the cake into 1/4 to 1/2-inch thick slices. Pan fry the nian gao in a nonstick pan over medium heat for 3 to 4 minutes, flipping halfway. The sides of the cake should brown and blister. You can also dip the slices of nian gao in an egg if you want some savory flavor. Whisk 1 egg with 1 tablespoon of water so that the egg can coat the nian gao evenly. Cook the nian gao for 3 to 4 minutes, flipping halfway.