Software process improvement methods help to continuously refine and adjust the software process to improve its performance (e.g., in terms of lead-time, quality of the software product, reduction of change requests, and so forth). Lean software development propagates two important principles that help process improvement, namely identification of waste in the process and considering interactions between the individual parts of the software process from an end-to-end perspective. A large shift of thinking about the own way of working is often required to adopt lean. One of the potential main sources of failure is to try to make a too large shift about the ways of working at once. Therefore, the change to lean has to be done in a continuous and incremental way. In response to this we propose a novel approach to bring together the quality improvement paradigm and lean software development practices, the approach being called Software Process Improvement through the Lean Measurement (SPI-LEAM) Method. The method allows to assess the performance of the development process and take continuous actions to arrive at a more lean software process over time. The method is under implementation in industry and an initial evaluation of the method has been performed.