In a small bowl, whisk together salt, MSG, ½ teaspoon five spice powder, 3 tablespoons dark brown sugar, and ground white pepper to combine. Set aside.

Using a paper towel, pat chicken thighs dry. Season chicken generously on all sides with salt mixture. Transfer to a wire rack set in a rimmed 13- by 18-inch baking sheet and refrigerate, uncovered, at least 8 hours and up to 72.

When ready to cook, adjust oven rack to middle position and preheat to 300ºF (150ºC). Using paper towels, pat chicken dry.

In a large cast iron or carbon steel skillet set over medium heat, heat vegetable oil until shimmering. Working in batches if necessary, add chicken, skin-side-down, and cook without moving until well-browned and crispy, 4 to 6 minutes. Flip chicken and cook lightly on second side, about 2 minutes. Transfer chicken to a large plate and set aside.

Reduce heat to medium-low. Add scallions, ginger, garlic, 1 teaspoon five spice powder, and 3 tablespoons dark brown sugar and cook, stirring, until vegetables are softened and starting to brown, 3 to 5 minutes. Add star anise, cassia bark or cinnamon stick, soy sauce, Shaoxing wine, and water, and bring to a simmer over medium heat.

Return chicken to pan skin-side-up, leaving the skin above the liquid but submerging most of the meat. Transfer skillet to oven and cook uncovered until chicken is cooked through and tender and registers at least 175ºF (79ºC), about 30 minutes.

Remove pan from oven. Serve with rice and vegetables, if desired.