[Your letterhead, if desired; if not, your return address]

[Date of letter-month, day, and year]

[Recipient's first and last names]
[Company name]
[Street or P.O. box address]
[City, State ZIP code]

Dear [recipient's name]:

It is with great pleasure that I wish you a wonderful National Bosses' Day! In the past two years since I started working for you, I have learned so much professionally and am grateful for all the ways I've been able to expand my career. Aside from that, you have been an excellent mentor and a wonderful person with whom to work.

I look forward to taking you to lunch this week to honor you on this special holiday. Thank you again for being an excellent boss.

Sincerely,

[Signature]

[Sender's first and last names]