Software product quality and project productivity require defining suitable software process models. The best process depends on the circumstances where it is applied. Typically, a process engineer tailors a specific process for each project or each project type from an organizational software process model. Frequently, tailoring is performed in an informal and reactive fashion, which is expensive, unrepeatable and error prone. Trying to deal with this challenge, we have built Casper, a meta-process for defining adaptable software process models. This paper presents Casper illustrating it using the ISPW-6 process. Casper meta-process allows producing project specific processes in a planned way using four software process principles and a set of process practices that enable a feasible production strategy. According to its application to a canonical case, this paper concludes that Casper enables a practical technique for tailoring a software process model.