Combine gochujang, honey, sake, light soy sauce, ground pepper and sesame oil in a mixing bowl. Add in the chicken drumsticks and toss to coat them thoroughly with the marinade.
Cover the mixing bowl and refrigerate for at least 4 hours, preferably overnight so that the chicken will be flavorful.
Preheat the oven to 400º F. Line a baking sheet with parchment paper and place the chicken drumsticks on top.
Bake the chicken drumsticks for 35 to 45 minutes in the center rack, until they are cooked through. If the skin is not crisp enough, move the chicken drumsticks to the top rack and turn on the broiler. Broil for about 5 minutes, watching the chicken drumsticks closely, until the skin is crispy.
Transfer the chicken drumsticks to a serving plate, sprinkle the toasted sesame seeds and chopped spring onion on top and serve with white rice, fried rice or fried noodles.