In a large bowl, whisk together the egg, flour, and milk. Then stir in the chopped chicken thighs and mix until thoroughly coated.
Heat the oil in a large skillet over medium heat. Carefully add the chicken and cook until golden brown and cooked through, about 8-10 minutes. Be gentle when stirring to help keep the breading from falling off. (You may want to cook in two batches depending on the size of your skillet.)
While the chicken is cooking, make the sauce by whisking together the chicken broth, soy sauce, brown sugar, rice vinegar, sesame oil, cornstarch, and garlic powder until well combined.
Once the chicken is crispy, pour the sauce overtop and allow to simmer until thickened, about 3-5 minutes.
Sprinkle sesame seeds over the top of the chicken. Serve warm over cooked rice.