01 - Whisk together rice flour, tapioca starch, water, salt, and 1/2 teaspoon oil in a mixing bowl until completely smooth. Allow batter to rest for 10 minutes to hydrate fully.
02 - Finely chop peeled shrimp into small pieces. Heat 1 tablespoon oil in a skillet over medium heat. Sauté minced shallot until fragrant, about 1 minute. Add chopped shrimp, salt, sugar, and pepper. Stir-fry until shrimp turn pink and moisture evaporates, 3-4 minutes. Remove from heat.
03 - Heat 2 tablespoons oil in a small pan until shimmering hot. Pour hot oil immediately over sliced scallions in a heatproof bowl. Stir gently and set aside to infuse.
04 - Bring water in steamer to a rolling boil. Lightly grease small ceramic dishes or ramekins (3-inch diameter). Restir batter and pour approximately 2 tablespoons into each dish, creating a thin layer. Arrange dishes in steamer basket, cover tightly, and steam for 7-8 minutes until cakes appear translucent and set. Remove and cool slightly before handling.
05 - Combine fish sauce, sugar, lime juice, water, and sliced chili in a small bowl. Whisk vigorously until sugar completely dissolves. Adjust balance to taste if needed.
06 - Top each steamed rice cake with a small portion of cooked shrimp mixture. Drizzle with scallion oil and sprinkle with crispy shallots. Add dollop of mung bean paste if desired. Serve warm with dipping sauce alongside.