I’ll never forget the Thanksgiving when the turkey didn’t finish in time for dinner. As a professional recipe developer, I knew how long to cook a turkey, but my experience must have made me flippant.

If you start roasting a 14-pound turkey at 375 degrees at 7 a.m. and need to feed 15 people — including three vegetarians, a vegan and two guests who are gluten-intolerant — by 1 p.m., how many pounds ...