01 - Whisk together rice flour, tapioca starch, water, salt, and 1/2 teaspoon oil in a bowl until completely smooth. Allow the batter to rest for 10 minutes to hydrate properly.
02 - Finely chop the peeled shrimp. Heat 1 tablespoon oil in a skillet over medium heat. Sauté the chopped shallot until fragrant, approximately 1 minute. Add the chopped shrimp, salt, sugar, and pepper. Stir-fry until shrimp are fully cooked and moisture has evaporated, creating a dry topping. Remove from heat and set aside.
03 - Heat 2 tablespoons oil in a small pan until hot but not smoking. Pour the hot oil over sliced scallions in a heatproof bowl. Stir gently to combine and set aside.
04 - Bring water in a steamer to a rolling boil. Lightly grease small 3-inch ceramic dishes or ramekins. Stir the rested batter and pour approximately 2 tablespoons into each dish, creating a thin layer. Arrange dishes in the steamer, cover, and steam for 7 to 8 minutes until cakes are set and translucent. Remove from steamer and cool slightly.
05 - Combine fish sauce, sugar, lime juice, water, and sliced chili in a small bowl. Stir continuously until sugar completely dissolves. Adjust balance to taste if needed.
06 - Place a small spoonful of shrimp mixture on each steamed rice cake. Drizzle with scallion oil, sprinkle with crispy shallots, and add mung bean paste if using. Serve warm with dipping sauce on the side.