"Michael, It was such a pleasure working with you. Thank you for all the additional information you provided me during this interview process and all the extra time you took to give me a mock interview and prepping me for my interviews. You provided me with so much useful information about the company and also resources I could use to gather even more information.
The extra preparation you and I did before hand really helped me stay calm and answer all the questions in a structured manner. Thanks you for the useful tips that I will alway keep with me when doing future interview. I would strongly recommend you to any of my friend and coworkers when they are searching for their next career move.
Keep up the outstanding work!"