01 - Whisk rice flour, tapioca starch, water, salt, and 1/2 teaspoon oil in a bowl until completely smooth. Allow batter to rest for 10 minutes to hydrate properly.
02 - Finely chop shrimp into small pieces. Heat 1 tablespoon oil in skillet over medium heat. Sauté shallot until fragrant, approximately 1 minute. Add chopped shrimp with salt, sugar, and pepper. Stir-fry until shrimp are fully cooked and moisture has evaporated, creating a dry topping consistency. Remove from heat.
03 - Heat 2 tablespoons oil in small pan until shimmering hot. Pour hot oil directly over sliced scallions in heatproof bowl. Stir gently and set aside to infuse flavors.
04 - Bring steamer water to rolling boil. Lightly grease small ceramic dishes or ramekins, approximately 3 inches in diameter. Stir rested batter and pour approximately 2 tablespoons into each dish, creating thin layer. Arrange dishes in steamer, cover, and steam for 7 to 8 minutes until set and translucent. Remove from steamer and cool slightly.
05 - Combine fish sauce, sugar, lime juice, water, and sliced chili in small bowl. Stir vigorously until sugar completely dissolves. Adjust balance if needed.
06 - Top each steamed rice cake with small portion of shrimp mixture. Drizzle with scallion oil and sprinkle with crispy fried shallots. Add mung bean paste if desired. Serve immediately while warm with dipping sauce alongside.