Cut tofu into 1 in. cubes and transfer to a plate. Dust with potato starch until all sides are coated.
In a large pan over high heat, add oil. Once oil is hot, add tofu and cook until golden on each side (about 5-7 minutes). Transfer to a paper towel to drain.
Add all sauce ingredients, except cornstarch, to a pan and bring to a boil. Lower heat to a simmer and slowly whisk in the cornstarch and water mix. Keep whisking until the sauce thickens. Turn off heat and stir in sesame oil, dried chilies and half of the scallions into the sauce.
Sprinkle leftover scallions on top of the tofu cubes and pour half of the sauce over. Add more sauce if needed.