Mix cornstarch with 3 tb stock. Combine 3/4 c stock, vinegar, sugar, ketchup, soy sauce, 1/2 ts salt, cayenne & black pepper in a bowl. Heat 1 tb oil in a small pot over a medium flame. When hot, toss in garlic & ginger. Stir. As soon as the garlic browns, remove pot from the heat & pour vinegar mixture from the bowl into it. Put pot back onto the heat & bring to a boil. Reduce heat & simmer for 4 minutes. Add cornstarch mixture. Stir till sauce thickens. Add more salt if required. Remove garlic & ginger. Put tofu cubes into a bowl. Add 2 ts salt to 6 cups water & bring to a boil. Pour boiling water over tofu. Let them sit for a while. Heat 2 tb oil in a wok. Put in 1/2 ts salt & carrot, peppers & scallions. Stir fry for 30 seconds. Turn off heat. Heat prepared sauce over a low heat. Take tofu out of the hot water. Squeeze gently to get rid of excess water & place on a serving platter. Spread vegetables over the tofu. Pour sauce over vegetables. Madhur Jaffrey, "World of the East Cookbook"