One-of-a-kind production (OKP) is a new manufacturing paradigm to produce customized products based on requirements of individual customers while maintaining the quality and efficiency of mass production. In this research, a computer-aided optimal product design and process planning approach is developed to support OKP product design and manufacture to satisfy individual customer requirements with near to mass production efficiency. In this work, a hybrid AND-OR graph is developed to model the variations of design configurations/parameters and manufacturing processes/parameters in generic product family. Since different design configurations and parameters can be created from the same customer requirements, and each design can be further achieved through alternative manufacturing processes and parameters, co-evolutionary genetic programming and numerical optimization are employed to identify the optimal product design configuration/parameters and manufacturing process/parameters. A case study to identify the optimal design configuration/parameters and manufacturing process/parameters of custom window products in an industrial company is introduced to demonstrate the effectiveness of the developed method.