MAKE THE CHICKEN. In a bowl, whisk the whites until frothy.
Add the salt, brown sugar and black pepper and whisk to combine.
Add the chicken and toss until well coated.
Add the cornstarch and baking powder and toss to combine; the mixture will become tacky.
Bring 4 cups of vegetable oil to 350 degrees in a frying pan or wok. Carefully drop the chicken pieces, one at a time, into the hot oil and cook in batches until the chicken is golden brown and the chicken is cooked through, for 3 to 5 minutes; drain on paper towels, then transfer to a large bowl.
Meanwhile, MAKE THE SAUCE. In a small saucepan, combine the peanut oil, garlic, red pepper flakes and scallions.
Cook over medium-high heat until the garlic begins to fry.
Add the sugar and stir until dissolved.
Add the ginger, chicken broth, sake, soy sauce and sesame oil and stir to combine.
In a small bowl, combine the cornstarch and 2 tablespoons of water; mix to create a slurry.
Add the slurry to the sauce and bring to a simmer and cook until thickened, for 2 minutes.
Pour the sauce over the chicken, add the sesame seeds and toss to coat; serve over white rice and garnish with scallions and a generous sprinkling of sesame seeds.