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 fully.
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 pink and slightly dry, 3-4 minutes. 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 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). 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 7-8 minutes until set and translucent. Remove dishes and let cakes cool slightly.
05 - Combine fish sauce, sugar, lime juice, water, and sliced chili in a small bowl. Stir vigorously until sugar completely dissolves. Adjust balance to taste.
06 - Top each steamed rice cake with a small spoonful of shrimp mixture, drizzle with scallion oil, sprinkle with crispy shallots, and add mung bean paste if desired. Serve immediately while warm with dipping sauce on the side.