We ask a participant to draw some screens of a product, thinking aloud. The participant can literally draw, or use blocks prepared beforehand, or cut out blocks from the screenshots of existing products, or edit a conceptual prototype. Usually, the participants are getting really involved into the process and recall many important details.
After the participant confirms everything is done, we ask why they have ignored the features and UI blocks that seems important to a project team. Often it shows that it's actually not relevant and can be safely removed from product.