Place the lemon zest, lemon juice, water, brown sugar, and buttermilk in a large mixing bowl. Whisk until the sugar dissolves completely and the marinade is smooth.
1 tbsp (6 g) freshly grated lemon zest, ½ cup (120 ml) fresh lemon juice, 1 cup (240 ml) water, 3 tbsps (38 g) packed light brown sugar, ⅓ cup (80 ml) buttermilk
Pierce each chicken drumstick several times with the tip of a fork to help the marinade penetrate the meat. Season lightly with kosher salt and black pepper. Add the drumsticks to the bowl and turn to coat evenly. Cover and refrigerate for at least 4 hours or preferably overnight, turning the chicken once or twice if possible.
12 (3½-4½ lbs / 1.6 - 2 kg) skin-on chicken drumsticks, kosher salt and freshly ground pepper
Remove the chicken from the refrigerator 20 to 30 minutes before baking so the drumsticks lose some of their chill.
Preheat the oven to 350°F (175°C).
Spread the panko breadcrumbs in an even layer on a baking sheet. Bake for 5 to 6 minutes, stirring once halfway through, until the breadcrumbs are lightly golden and dry. Remove from the oven and allow them to cool slightly.
2 cups (100 g) Panko breadcrumbs
Increase the oven temperature to 400°F (200°C).
Transfer the toasted panko to a large resealable plastic bag or shallow dish. Add the olive oil, dried thyme, lemon zest, cayenne pepper, kosher salt. Toss until the breadcrumbs are evenly coated with the oil and seasonings.
2 tbsps (30 ml) olive oil, 2 tsps (2 g) dried thyme leaves, 1 tbsp (6 g) freshly grated lemon zest, ½ tsp (1 g) cayenne pepper, 1 tsp (5 g) kosher salt
Place the mayonnaise in a small bowl. Spread a thin, even layer of mayonnaise over each drumstick. The mayonnaise helps the panko adhere evenly and encourages browning in the oven.
½ cup (120 g) mayonnaise
Place each drumstick into the seasoned panko mixture and shake or roll until fully coated. Arrange the drumsticks on a wire rack set over a baking sheet, leaving space between each piece.
Lightly mist the drumsticks with olive oil cooking spray.
olive oil cooking spray
Bake for 35 minutes. Carefully turn the drumsticks and continue baking for 35 to 40 minutes, until the coating is deeply golden and the chicken reaches an internal temperature of 175°F (79°C) near the bone.
Allow the chicken to rest for 5 minutes before serving.