Preheat water to 155°F using Anova sous vide precision cooker.
In the meantime, season chicken drumsticks with salt and pepper. Place chicken in the sous vide bag in one layer and seal using a vacuum sealer or a hand pump.
Once the water is ready, slowly lower the chicken into the prepared water bath. Make sure the chicken drumsticks are completely under the water. Cook chicken for 2 hours.
Once the chicken is done, remove the bag from the water bath and drop it into an ice bath to fully chill. (This step will help get extra-crispy skin when you sear it without overcooking the chicken underneath.)
Remove the chicken from the sous vide bag and scrape off any gelled juices using your fingers. (You may preserve the chicken juice for soups or other uses).
Pat the chicken with paper towels. Heat a nonstick pan or cast-iron skillet over high heat on the stove, sear the chicken for 1-2 minutes on each skin side or until the skin is golden brown and crispy. Transfer the chicken to a plate and set aside.
In the same pan, whisk all Chinese sauce ingredients over medium heat until well combined. Turn off the heat.
Stir in the chicken drumsticks and coat them with the Chinese sticky sauce. Dish and sprinkle with white sesame seeds and chopped green onions over. Enjoy!