Come September, don’t expect to find chef Lydia Shire behind the line at Excelsior. She’ll be handing over the day-to-day operations so she can devote her energies to working on a cookbook, which she’s been eager to get started on for a while. Although Shire anticipates being actively involved in the development of the restaurant’s creative content in the future, chef Eric Brennan, currently of the Harvest in Cambridge, will be taking culinary reins. Having earned himself a loyal following and rave reviews in Cambridge, Brennan is undaunted by the size of the shoes he has to fill and “looking forward to continuing what Lydia created, and adding my own sensibility too.”