Special equipment: mortar and pestle or a spice grinder
For the ground toasted rice: Toast the rice in a dry skillet over medium heat, shaking the pan occasionally, until it just begins to turn golden, 3 to 5 minutes. Transfer to a plate to cool. Grind the rice to the texture of coarse cornmeal in a mortar and pestle or spice grinder.
For the roasted chiles: Heat the oil to 350 degrees F. in a large saucepan. Add the chilies and fry until dark red in color, 1 to 2 minutes. Don't allow them to burn. Drain on paper towels. Grind the chiles in a mortar and pestle or with a spice grinder until they are broken up into very small pieces. Store in a sealed container.
Slice the fish skin into strips and put it in a small bowl. Add the cornstarch, salt, pepper, 1 tablespoon of the ground toasted rice and 1/2 teaspoon of the roasted chiles. Toss to coat and set aside. Heat some oil in a saucepan to 350 degrees F. Deep fry the fish skin until crispy. Drain on paper towels.
Cut the fish into thin slices. Lay them out on a plate. Squeeze the juice of 2 limes over the fish. Set aside for 7 to 10 minutes to cook.
For the sauce: Combine the lemongrass, chile, basil, cilantro, mint, sugar, salt and 1 teaspoon roasted chiles, and grind in a mortar and pestle or a spice grinder until the mixture forms a paste. Stir in the fish sauce and lime juice.
For the dipping salt: Combine the salt, pepper, sugar, 1 tablespoon of the ground toasted rice powder and 1 tablespoon of the roasted chiles in a small bowl. Stir to combine. Reserve the remaining ground toasted rice and roasted chiles for another use.
Spoon the sauce over the fish. Garnish with some of the fried fish skin.
Serve the dipping salt with the remaining fried fish skin. Serve immediately.