01 - Whisk together 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 the peeled shrimp. Heat 1 tablespoon oil in a skillet over medium heat. Sauté chopped shallot until fragrant, approximately 1 minute. Add chopped shrimp, salt, sugar, and pepper. Stir-fry until shrimp are fully cooked and moisture has evaporated, creating a dry topping consistency. Remove from heat and set aside.
03 - Heat 2 tablespoons vegetable oil until shimmering hot. Pour hot oil directly over sliced scallions in a heat-resistant bowl. Stir gently and set aside to infuse.
04 - Combine fish sauce, sugar, lime juice, water, and sliced chili in a small bowl. Stir vigorously until sugar completely dissolves. Adjust proportions to taste preference if needed.
05 - Bring water in steamer to a rolling boil. Lightly grease 3-inch diameter ceramic dishes or ramekins. Restir batter to redistribute settled starch. Pour approximately 2 tablespoons batter into each greased dish, creating a thin layer. Arrange dishes in steamer basket, cover tightly, and steam for 7 to 8 minutes until cakes are set and translucent. Remove from steamer and cool slightly before unmolding.
06 - Top each steamed rice cake with a small portion of cooked shrimp mixture. Drizzle with scallion oil and sprinkle generously with crispy fried shallots. Add mung bean paste if desired. Arrange cakes on serving platter and accompany with dipping sauce. Serve immediately while warm.