Model Driven Development (MDD) is an emerging paradigm for software construction that uses models to specify programs, and model transformations to synthesize executables. Feature Oriented Programming (FOP) is a paradigm for software product lines where programs are synthesized by composing features. Feature Oriented Model Driven Development (FOMDD) is a blend of FOP and MDD that shows how products in a software product line can be synthesized in an MDD way by composing features to create models, and then transforming these models into executables. We present a case study of FOMDD on a product line of portlets, which are components of web portals. We reveal mathematical properties of portlet synthesis that helped us to validate the correctness of our abstractions, tools, and specifications, as well as optimize portlet synthesis.