Birthday lunch with Mom on UWS, UES or Midtown?
Felidia is amazing and I think it has a reasonably priced prix fixe lunch (or at least used to). Otherwise, midtown has a million amazing "special occasion" restaurants --- some of my favorites are Le Bernardin, the Modern, and Jean Georges. They're elegant and certainly upscale, but not too stiff or corporate/power lunch-y. Of the three, I find I can relax more easily at Le Bernardin and Jean Georges-- not sure if it's the color scheme or the service, but there it is.