Whisk broth, soy sauce, hoisin, 1 teaspoon cornstarch, ginger, vinegar, brown sugar, white pepper, and red pepper flakes together in a small bowl. Set sauce aside.
Place remaining cornstarch in a resealable, zip-top plastic bag. Tear off bite-sized chunks of tofu and drop them into the bag. Shake until each piece is evenly coated. Sprinkle on cornstarch by hand, if needed, to coat each piece well.
Heat oil in a wok or large nonstick skillet over medium-high heat until hot. Add tofu pieces one by one and cook until golden brown. Use a slotted spoon to move and turn the pieces until browned on all sides, 10 to 15 minutes. Transfer to a plate lined with paper towels.
Pour out any remaining oil. Add the white parts of the green onions and cook until fragrant, about 1 minute. Pour in the sauce. Allow to heat and thicken, about 2 minutes. Return the tofu to the wok and toss to coat. Discard ginger. Garnish with green onion tops, peanuts, and sesame seeds.