01 - Whisk together rice flour, tapioca starch, water, salt, and 1/2 teaspoon oil in a bowl until smooth. Allow the batter to rest for 10 minutes to ensure proper hydration.
02 - Finely chop the shrimp. Heat 1 tablespoon oil in a skillet over medium heat. Add the shallot and sauté until fragrant, about 1 minute. Add chopped shrimp, salt, sugar, and pepper. Stir-fry until shrimp are cooked through 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. Mix gently and set aside to infuse.
04 - Bring water in a steamer to a boil. Lightly grease small ceramic dishes or ramekins (3-inch diameter). Stir the 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 and let cool slightly before handling.
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 if needed.
06 - Top each rice cake with a spoonful of shrimp mixture, drizzle with scallion oil, and sprinkle with crispy shallots. Add mung bean paste if using. Serve immediately while warm with dipping sauce on the side.