In the mixing bowl, stir rice flour, tapioca starch, room-temperature water, and lemon juice thoroughly. Cover the bowl with plastic wrap and let the batter rest at room temperature for at least 1 hour.
In the skillet, sauté minced shallots and minced garlic in oil until fragrant.
Add minced pork and cook for 2 minutes. Stir constantly. Add minced shrimp and continue stirring.
Add annatto powder, sugar, black pepper, fish sauce, and some water to the skillet.
Dissolve tapioca starch in a small amount of room-temperature water and add the mixture slowly to the skillet. Stir well to combine. Cook for another 2 minutes.
Stir the batter thoroughly while slowly adding hot water to the bowl. Add vegetable oil to the batter.
Put the filled steamer on the stovetop. Turn the heat to high and bring the water to a boil. Preheat the small dishes in the basket for 3 minutes.
Fill each dish with a suitable amount of batter. Put on the lid and steam for 7 minutes. Take the dishes out of the steamer. Repeat the process until the batter runs out.
Top each rice cake with some fried shallots, scallions and oil garnish, and bits of the pork and shrimp mixture. Serve with the garlic chili sauce on the side.