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 shrimp into small pieces. Heat 1 tablespoon oil in a skillet over medium heat. Sauté the chopped shallot until fragrant, then add the shrimp, salt, sugar, and pepper. Stir-fry until the shrimp are fully cooked and the mixture appears slightly dry. Remove from heat and set aside.
03 - Heat 2 tablespoons oil in a small pan until shimmering hot. 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 rested batter and pour about 2 tablespoons into each dish, creating a thin layer. Arrange dishes in the steamer, cover, and steam for 7 to 8 minutes until the cakes are set and translucent. Remove and 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 proportions 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. Arrange the cakes on a serving platter and serve warm with the dipping sauce alongside.