Reflection is essential for professional competence development in every profession. Reflection-"on"-action (taking place a posteriori, when the task is already accomplished) and reflection-"in"-action (occurring while performing the task) are equally important to increasing one's professionalism. Some evidence supports the effectiveness of promoting the former by using metacognitive prompts that encourage vocational education apprentices to reflect. However, it is unclear to what extent this approach is effective to promote their reflection-"in"-action, to increase the quality of their professional performance, and to establish a long-term attitude to reflect "on-action." Using a thinking aloud technique, we asked 15 apprentice chefs to cook a recipe and video-recorded them. When finished, we asked them to complete a report that self-assessed their performance. Nine of them were accustomed to metacognitive prompts to reflect on their practice, the others not. The former group outperformed the latter in the quality of their reflection-"in"-action. Also, the quality of their performance, according to two experts' assessment, was significantly better. Finally, their reflection-"on"-action was higher. Despite its limitations due to the small sample, the study represents a good premise to confirm the effectiveness of our pedagogical approach and transfer it to other initial vocational education professions.