I'm late 30s, entrenched in the corporate world, have been promoted multiple times despite my stutter. I, too, stutter most in front of my managers, but not nearly as much as I used to. I think the stutter is less of an issue now because of a change in my confidence and, thus, my anxiety. I'd recommend, prior to speaking with your boss, to briefly say to yourself "my boss likes me, my boss loves me, i love talking to my boss." Say it to yourself as often as you can. You may be fooling yourself right now by saying "i love talking with my boss" but in time, maybe it will be true. You are already off to a good start because you know he likes you, so that should be a confidence booster right there. I've actually told my latest boss how weird it is that I stutter most with him, probably because he has the most control over my paycheck. Little self-disclosures like that slowly chipped away at my stutter, and strengthened my relationship with my boss at the same time (it doesn't hurt to let him feel that he has a certain power over me). Another thing that works is Toastmasters. Look for your nearest club. Mine meets at lunchtime on a weekday. My boss knows I attend and I assume he understands its value to me and the company.