The article presents a new tool for designing product interfaces with input from end-users. This tool allows users to create custom interfaces for household appliances based on their own needs and experiences. Designers provide constraints like color limitations and interface geometry, but users have the freedom to design as they wish. By analyzing user choices, designers can better understand user needs and preferences. The tool also allows for immediate usability testing using a Mixed Reality prototype. The study shows that this tool can effectively support the design of product interfaces during participatory design sessions.