01 - Whisk together rice flour, tapioca starch, water, salt, and 1/2 tsp oil in a bowl until completely smooth. Let the batter rest for 10 minutes to allow proper hydration.
02 - Finely chop the peeled shrimp. Heat 1 tbsp 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 slightly dry, approximately 3-4 minutes. Remove from heat and set aside.
03 - Heat 2 tbsp oil in a small pan until hot but not smoking. Pour the hot oil over the sliced scallions in a heatproof bowl. Stir gently to combine and set aside to infuse.
04 - Bring water in a steamer to a boil. Lightly grease small ceramic dishes or ramekins (approximately 3-inch diameter). Stir the batter briefly and pour about 2 tbsp into each dish, creating a thin layer. Arrange dishes in the steamer, cover, and steam for 7-8 minutes until the cakes are set and translucent. Remove and let cool slightly before handling.
05 - Combine fish sauce, sugar, lime juice, water, and sliced chili in a small bowl. Stir vigorously until the sugar completely dissolves. Adjust flavors to taste if needed.
06 - Top each steamed rice cake with a small spoonful of the cooked shrimp mixture. Drizzle with scallion oil, sprinkle with crispy shallots, and add mung bean paste if using. Serve immediately while warm with the dipping sauce on the side.