Place the block of tofu between stacks of paper towels, weigh down with a plate and leave for ten minutes.
Cut the tofu into two-inch cubes.
Place the cubed tofu in a bowl, add the starch and toss gently to coat every inch of the surface.
Heat enough cooking oil in a wok to reach a depth of at least an inch and a half (more is better).
Fry the tofu cubes, turning them over for even frying, until a crispy crust forms on the surface.
Scoop out the tofu and drain on a rack.
Cook the sauce
In a clean wok or frying pan, stir together all the ingredients for the sauce.
Set the heat to medium and cook the sauce, stirring, until thickened and no longer cloudy.
Set the heat to medium-low and continue cooking the sauce until reduced and thick enough for a canal to form when you drag a spatula across the bottom of the pan.
Taste the sauce. Depending on whether the chicken broth is unseasoned or lightly seasoned, you may need to add salt to balance with the sweetness.
Assemble the dish
Dump the fried tofu cubes into the sauce.
Toss repeatedly until the tofu cubes have soaked up most of the sauce.
Garnish with cilantro and toasted sesame seeds before serving.