A 58-year-old patient presented with a dislodged crown and post and core on the maxillary right first premolar. After endodontic retreatment, two tapered glass-fiber posts were adhesively cemented. The core foundation was completed by retrofitting the existing crown with a self-curing composite core material. The intaglio surface was lubricated with petroleum jelly, which allowed for easy removal of the crown. Adequate cement thickness was ensured by the finishing procedures of the core buildup that respected the existing tooth margins. The glass-fiber posts and composite buildup provided adequate stability and retention to the original casting. The technique described in this short clinical report enables clinicians to rebuild a post-and-core foundation using the existing crown without the original die or its replica in a simple and time-saving way.