Blockchain is an emerging technology that facilitates the elimination of intermediaries or third parties, thereby reducing costs and enhancing efficiency. Over the past decade, blockchain has been integrated across various industries, yet its wide-scale adoption within the financial industry remains uncertain. This paper seeks to aid financial institutions in adopting blockchain technology by developing a maturity model. This model is intended to assist organisations in assessing their current maturity level and charting a way forward towards a more enhanced adoption of the technology. We construct an initial model based on literature on existing maturity models in other fields of study. Subsequently, we refine the model through the Delphi approach which is a qualitative, systematic, and iterative panel method. We conduct the Delphi method in three rounds with experts in the field, yielding a final maturity model and a corresponding questionnaire which allows financial institutions to conduct a self-assessment of their blockchain adoption capabilities. We discuss the validity of the model and provide a proof of concept through a self-assessment exercise by a participating institution. The panel participants and contributing institutions concurred that the resulting maturity model and the corresponding self-assessment questionnaire are relevant and useful tools for the purpose of assessing their current maturity and informing future actions to enhance their blockchain adoption capabilities.