what if your supervisor asks you to write your own recletter

don't do it. In the worst case, ask a friend to write it for you and have your recommender edit it. Do not write it yourself.

I know that this problem exists. But it is better to ask him that you are comfortable waiting for longer duration to get the letter written by him whenever he finds time available. But it will slow down your application ( I am still waiting for one of my recommenders to submit his letter for Columbia ED, whereas I have completed my Col application around 10th Sep).

I ran into this problem too. Thing was, it was the same recommender who had offered to write me one. Oy.

Honestly, I don't see a huge ethical problem in writing/outlining a recommendation and then your boss editing it before signing and sending it on. It's not the way I'd prefer to do it, of course. And if you have ready alternatives, it might be better to go with them. But if you don't... eh. I think the ability of adcoms to recognize your "writing style" is overestimated. They do read thousands of essays, of course, and if your writing style is sufficiently sophisticated (i.e. doesn't include obvious errors of grammar, spelling and awkward sentence structure), I doubt they'll notice.

Still, when I'm a big important person who gets recommendation requests eventually, I'll make it a point never to ask a subordinate to write their own. I just think it's tacky.