Blanch the bean curd in boiling water for 1 minute. Drain and cut into 5mm (1/4 inch) cubes).
Heat the oil in a pan and add the onion and garlic. Stir-fry for 1 minute, then add the beef. Stir fry until the beef is evenly browned. Add the bean curd, chili peppers, sugar, and soy sauce. Bring to the boil.
Add the cornstarch mixture and simmer, stirring, until the sauce has thickened. Serve hot.
Very similar to Ma Po Bean Curd, but without the black beans, drier, and less complicated in general.
The Complete Encyclopedia of Chinese Cooking, Kenneth Lo et al.