Add a small pinch of salt and sesame oil to minced meat. Mix well and set aside.
Mix 1 tablespoon of cornstarch with 2 and 1/2 tablespoons of water in a small bowl to make water starch.
Cut tofu into square cubes (around 1/2 inch). Bring a large amount of water to a boil and then add a pinch of salt. Slide the tofu in and cook for 1 minute. Move out and drain.
Get a wok and heat up around 2 tablespoons of oil, fry the minced meat until crispy. Transfer out beef out and leave the oil in.
Add garlic, scallion white and ginger to cook for 30 seconds until aroma. Then mix pepper flakes in.
Add water to the seasonings and bring to boil over high fire. Gently slide the tofu cubes. Add soy sauce, sake and beef. Reduce the heat after boiling and then simmer for 6-8 minutes. Then add chopped scallion greens.
Stir the water starch and then pour half of the mixture to the simmering pot. Wait for around 30 seconds and then pour the other half. You can slightly taste the tofu and add pinch of salt if not salty enough. If you feel it is too spicy, add some sugar can milder the taste. But be carefully as the broth is very hot at this point.
Transfer out when almost all the seasonings stick to tofu cubes. Sprinkle Sichuan peppercorn powder (to taste)and chopped garlic greens if using.
Serve immediately with steamed rice.