Rinse the drumsticks and pat them dry with paper towels; set aside.
Trim the bottom 2 inches (5 cm) of cilantro stems, then pound in a mortar and pestle and squeeze to extract the juice; reserve 1 tablespoon.
In a large mixing bowl, whisk together the shrimp sauce, sugar, egg white, sesame oil, cilantro stem juice, cornstarch, and all-purpose flour until smooth.
Add the chicken to the marinade and toss to coat thoroughly; cover and refrigerate for at least 4 to 6 hours.
When ready to cook, heat enough oil in a deep pot or fryer to deep-fry the drumsticks until it reaches about 350–375°F (175–190°C).
Carefully lower the marinated drumsticks into the hot oil and fry until golden brown and cooked through, about 8–12 minutes depending on size.
Transfer the fried chicken to a plate lined with paper towels to drain excess oil, then serve immediately with chili sauce on the side.