Preheat oven to 450F, and spray a baking rack with cooking spray.

Cut the cauliflower into 1- to 2-inch chunks. In a bowl, mix the cornstarch, baking soda, salt, white pepper, and sesame oil with 3/4 cup of the rice flower.  Add water gradually and stir until a you get a crumbly, almost gritty batter.  You want it to be more like a moist, powdery coating rather than a thin batter.  Think wet beach sand.

Toss in the cauliflower and mix with batter until it is evenly coated.  At that point, sprinkle the remaining rice flower over the cauliflower and mix so that all the dry flour is sucked up by the batter.

Arrange cauliflower on the backing rack, leaving space between the florets.  Cook on the center rack of your oven for 25-30 minutes, until the cauliflower brown and crispy.  We started to smell it after 20 minutes, and it was nicely browned after 30 minutes.

In large saucepan, mix chicken stock, sesame oil, soy sauce, and vinegar.  Stir in ginger, garlic, chili pepper flakes, and sugar, and bring to a simmer over low-medium heat, stirring occasionally.

Mix cornstarch and cold water and pour into simmering sauce, stirring constantly until it has thickened.  Now, add the baked cauliflower to the saucepan and gently mix it with the sauce until completely coated with the sauce.  

Garnish with green onion or sesame seeds if desired, and serve immediately.