I interviewed a few weeks back, was told on the spot that the job was mine. It has been 2 weeks and although I was sent their benefit package, I have yet to receive an official written offer. How do I go about asking for one?
How do I go about asking for one?
You just ask.
Something like "I'm excited about working with you. Once I receive a formal offer letter, I can sign and return it. Then I will hand in my resignation at my current company and we can set a starting date. When do you think I should expect to receive the letter?" should suffice.
That way, you aren't pushing them to get you the letter faster. You are just asking when you should expect to receive it, and reinforcing the fact that you need the letter to move forward.
It's polite, yet still gets the point across.
A friend had a situation where a job offer was significantly delayed following a verbal offer. It turned out the terms of the position had changed and the organization was attempting to salvage the situation and work out an alternative arrangement that would allow to bring him on board.
In that situation, rushing things would not have helped and may have added tension to the situation, whereas the organization simply needed more time to make proper arrangements before the offer could be finalized. In the end, he felt confident enough in the job that he actually began relocating before he had the offer letter in hand. He ended up receiving the letter and things worked out fine, but nevertheless it was a risky move (no pun intended).
Things can and do go wrong at the last minute for any of a number of reasons. Do make sure you have a formal offer letter before turning in your 2 week notice, or showing up to 1st day of work!
Also, HR departments at employers of different type (e.g. govt vs. private) and size do not move at the same speed. In some places there is more internal paperwork and hoops to jump through, in some places less.
Bottom line, I agree you should just ask, but make sure asking does not begin to resemble nagging: space it out by about a week, but remain firm that you would actually need a formal letter before you can give the 2 week notice to your current employer, so they can plan for additional delay on your end before the start date. Good luck!