Mixed Reality (MR) and Intangible Cultural Heritage (ICH) are gaining momentum in museum settings, yet we rarely see a combination of the two. MR can leverage established tangible user interfaces (TUI) in museums while amplifying the living performative nature of ICH. MR for ICH requires purposeful research and inquiry by interaction designers who must work in cooperation with CH professionals and local communities. To this end, this paper presents a four‐phase framework for (co)designing MR installations that convey ICH in museums, which defines the following phases: First, Field Inquiry embeds designers within ICH communities, combining ethnographic observation and interviews, to distil essential knowledge of tacit skills and cultural narratives. Next, Open‐brief co-design invites craftspeople, museum staff, and potential visitors to collaboratively ideate early concepts, often through embodied methods. Then, in the Prototype‐led co-design stage, iterative refinements, supported by mid‐ to high‐fidelity prototyping, ensure that tangible elements align with museum constraints and user expectations. Finally, Evaluative co-design encompasses iterative lab‐based and on‐site evaluation methods (questionnaires, interviews, user observations), producing data‐driven insights on usability, user experience, and learning outcomes. The proposed framework is presented not only in theory but in the practice of designing MR installations, with a representative ICH case: Tinian marble craftsmanship. The proposed framework contributes a replicable, human‐centred approach to designing MR exhibits for ICH, emphasising participatory methods, bodily interaction, and layered storytelling. It addresses both technical feasibility and cultural authenticity, offering a methodological roadmap for museums and designers seeking to embed intangible practices in interactive installations.