How to Make It
In a large bowl, cover the rice with 2 inches of cold water and let soak for at least 8 hours or overnight.
Heat a large wok or nonstick skillet over high heat. Add the guajillo chiles, reduce the heat to low and cook, stirring, for 2 minutes. Add the chiles de árbol and cook, stirring, until the chiles are very dark, about 3 minutes longer. Transfer the chiles to a spice grinder and let cool, then grind coarsely. Transfer to a medium bowl. In a small bowl, stir the palm sugar with the boiling water until the sugar dissolves. Stir 3 tablespoons of the syrup into the ground chiles; discard any remaining syrup.
In a mortar or food processor, pound or pulse the lemongrass to a coarse puree. Add half of the lemongrass to the chile mixture along with the lime juice, fish sauce, soy sauce and Thai seasoning sauce. Let stand at room temperature for at least 1 hour or refrigerate for up to 2 days. Bring to room temperature before serving.
Preheat the oven to 325°. Drain 2 tablespoons of the rice and spread out on a small foil-lined baking pan. Bake, stirring occasionally, until light golden brown, 10 to 12 minutes. Let cool, then process in a spice grinder until finely ground.
Add the garlic and salt to the remaining lemongrass in the mortar or food processor and pound or pulse to a chunky paste. Set the catfish on a baking sheet and score down to the bone at 1-inch intervals. Rub the lemongrass paste all over the fish, inside and out.
Light a hardwood charcoal fire and rake the coals to one side. Grill the fish over indirect heat (opposite the coals), covered, until cooked through, 45 minutes to 1 hour; you may need to add hot coals periodically to maintain the heat. Alternatively, roast the fish in a 350° oven for about 35 minutes, until it is cooked all the way through and flakes easily.
In a wok, bring 3 inches of water to a boil. Line a bamboo steamer with a double thickness of cheesecloth. Drain the remaining rice in a colander and set the colander in a large bowl. Fill the bowl with cold water and gently stir the rice; the water will become cloudy. Lift the colander from the bowl and pour out the water. Repeat this process until the water runs clear. Spread the rice in the steamer in an even layer and fold the overhanging cheesecloth over it. Cover the steamer and set it in the wok. Steam the rice until tender, about 15 minutes; halfway through steaming, using 2 tongs, carefully flip the rice over in the cheesecloth. It should be tender but chewy when done. Transfer the rice to a bowl, cover and let stand for 15 minutes.
Transfer the catfish to a platter. Stir the toasted rice powder and cilantro into the jaew sauce and serve with the fish and sticky rice.