Take 4 eggs out of your refrigerator and place them in a bowl of warm water for 10 minutes, dry them with a paper towel, and set aside so they can air dry.
Spray an 8 cup (2 quart) capacity bowl or large casserole with a nonstick cooking spray (or line with parchment paper squares), set aside.
Set up your steamer with at least 1.5 inches of water and boil the water at low heat while you make the cake.
Mix the flour, rice flour, baking powder, and baking soda in a medium size bowl with a fork or a whisk.
Separate the egg whites and egg yolks into two large mixing bowls.
Use an electric mixer to whip the egg whites slowly until they start to foam, gradually increase the speed and keep beating until the egg whites start to form swirls and stiff peaks.
Add cream of tartar and keep mixing for another minute, set aside.
Beat the egg yolks, add brown sugar, and mix until fully incorporated.
Add oil, mix.
Add evaporated milk, mix.
Add vanilla extract, mix.
Add about half of the flour mixture and mix the batter on low speed, add the remaining flour, and mix.
Check that the steamer has enough water to steam for one hour (at least 1.5 inches of water, add water if needed) and that it is boiling at medium to medium high heat.
Add the egg whites to the cake batter and use a spatula to gently fold in the egg whites until the batter looks even.
Transfer the cake batter to the large bowl that has been prepared for steaming, gently smooth the batter with a spatula so that it's even (refrain from tapping the bowl), and place in the steamer.
Meanwhile place a piece of cheesecloth on the steamer, place the steamer lid on top of it, and secure all the edges and corners with a clothespin or two,and steam the cake for one hour (do not get distracted during this step!).
ALTERNATIVELY if you have safety concerns regarding using cheesecloth on a gas stove or don't have cheese cloth, steam the cake for one hour and then lift the lid quickly and be careful not to allow any condensation to drip onto the cake.
You can serve the cake warm or at room temperature, in 2-3 inch sized rectangular or parallelogram shaped blocks.