Grate the white part of the lemongrass with a microplane or finely chop it with a sharp knife.
In a mixing bowl, combine the grated lemongrass, honey, salt, ground black pepper, and cayenne pepper if using.
Add the boneless skin-on chicken thighs to the bowl and toss to coat evenly with the marinade; let sit for 10–15 minutes.
Heat a little oil in a skillet over medium heat until shimmering.
Place the chicken in the skillet skin-side down and pan-fry until the skin is nicely browned and crispy, about 4–6 minutes.
Flip the chicken and continue to pan-fry until the meat is cooked through and browned, about 3–5 more minutes; ensure no pink remains.
If desired, finish under the oven broiler for about 1 minute to char the surface; watch carefully to avoid burning.
Remove from heat and serve immediately with steamed rice or preferred sides.