If your wings are frozen, thaw them completely in the fridge first. Pat the wings dry. In a large bowl, toss the wings with the cornstarch, flour, soy sauce, 1 teaspoon salt, 1 teaspoon sugar and 2 teaspoons white pepper until every wing is lightly coated. Cover and refrigerate for at least 2 hours. Wash your hands, the cutting board and any tools that touched the raw chicken with hot soapy water, and keep the raw wings away from the finished ones. Don't rinse the chicken. Use separate tongs or strainers for raw and cooked wings.
Toast the glutinous sweet rice in a dry pan over medium heat, stirring constantly, until golden brown and nutty. Let it cool for a few minutes, then tip it into a high-speed blender with the 2 tablespoons salt, MSG, vinegar powder, 1 teaspoon sugar, 2 teaspoons white pepper and Hat Nem seasoning. Blend until fine. Measure out 2 teaspoons for the wings and keep the rest in an airtight container.
Heat the 5 cups oil in a wok or deep pot (no more than half full) over medium-high heat to 375°F (190°C). In small batches, lift each wing from the bowl, shake off the loose coating and lower it slowly into the oil, away from you. Fry the wings about 5 to 7 minutes until pale gold and cooked through. Times vary with wing size and oil temperature. The oil temperature dips when the wings go in, so adjust the heat to keep it around 350 to 375°F. Check the largest wing of each batch at the thickest part, away from the bone, with an instant-read thermometer: it must reach 165°F (74°C). Keep frying any wing that is under 165°F. Rest the wings on a wire rack about 10 minutes and turn the heat to low during the rest.
Bring the oil back to 375°F (190°C) and fry the wings a second time, a few at a time, about 2 to 3 minutes until deeply golden and crisp. Drain on the wire rack.
Pat the sliced lemongrass dry and add it to the same hot oil in small handfuls, standing back, because it will bubble up. Fry until golden and crispy. Fish it out with a strainer, drain and set aside. Turn off the heat and leave the pot where it is, away from kids and pets. Never move hot oil. Let it cool while you finish the next step.
Heat 3 tablespoons of fresh oil in a second clean, dry wok or pan over high heat until shimmering. Add the garlic and jalapeño and stir 2 to 3 times. Tip in the double-fried wings, add the crispy lemongrass and 2 teaspoons flavour powder, and toss until every wing is coated. Plate right away and serve hot.
Once the frying oil is completely cold, which takes a couple of hours, strain it into a sealable container and put it in the trash, or take it to a local oil recycling drop-off. Check your local rules. Never pour it down the drain.