01 - Whisk together rice flour, tapioca starch, water, salt, and 1/2 teaspoon oil in a mixing bowl until completely smooth. Let the batter rest for 10 minutes to allow proper hydration.
02 - Finely chop the peeled shrimp. Heat 1 tablespoon oil in a skillet over medium heat. Sauté the chopped shallot until fragrant, about 1 minute. Add the chopped shrimp, salt, sugar, and pepper. Stir-fry until shrimp are fully cooked and moisture has evaporated, creating a dry crumble texture. Remove from heat and set aside.
03 - Heat 2 tablespoons vegetable oil until hot but not smoking. Pour the hot oil over sliced scallions in a small heatproof bowl. Stir gently and set aside to infuse.
04 - Bring water in a steamer to a rolling boil. Lightly grease small ceramic dishes or ramekins (about 3-inch diameter) with vegetable oil. Stir the rested batter and pour approximately 2 tablespoons into each dish, creating a thin layer. Arrange dishes in the steamer, cover tightly, and steam for 7 to 8 minutes until set and translucent. Remove carefully and let 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 - Top each steamed rice cake with a spoonful of shrimp mixture, a drizzle of scallion oil, and a sprinkle of crispy shallots. Add mung bean paste if using. Serve immediately while warm with dipping sauce on the side.