A landmark Boston restaurant is closing after four decades in business. L'Espalier is shutting its doors and it will serve its final patrons tonight.

L'Espalier owner and chef Frank McClelland says the restaurant's lease was up - at a spot adjacent to the Mandarin Oriental hotel on Boylston Street - and the time was right to move on to other opportunities.

"I wanted to leave on top after all these years, and did not want to risk not being perfect or chasing perfection on a daily basis," said McClelland.

Legendary chef Moncef Meddeb opened L'Espalier in 1978. McClelland worked under him for three years, starting in 1980.

Eight years later - after McClelland had left L'Espalier - Meddeb called him and said he was selling the restaurant. McClelland bought L'Espalier, and has been its head chef and owner ever since. He took things in a new direction.

"I kind of set my sights on developing relationships with local farms in Vermont, New Hampshire, Maine and Massachusetts - developing up a cuisine that was very much New England and sourced from New England, with European sensibilities," said McClelland.

This local sourcing saturates L'Espalier's offerings. The restaurant has ever-changing lunch, dinner and bar menus, with options to order food "a la carte" or sign up for multi-course tasting meals. Items like butter poached Maine lobster, honey roasted duck breast, foie gras and New England-sourced sirloin are just some of the choices on the L'Espalier menu.

McClelland says the menu is just a part of what sets L'Espalier apart from other restaurants.

"People ask me how do you maintain such a high level for so long and I tell everyone it's 99-percent hard work every day, keeping your eye on the ball, and putting together a really wonderful team that loves each other and subsequently loves the guest," said McClelland.

Over the years, L'Espalier has hosted guests from all walks of life - regular joes and celebrities alike - people like Julia Child, Henry Kissinger and Mick Jagger, even David Ortiz and Bill Belichick have stopped by. McLelland says all guests - regardless of stature - are treated the same when they walk through the door.

"I do get a kick out of that, but I've never actually taken a picture with anyone or done anything like that, because I try to protect their space, and that they have the complete L'Espalier experience so I've always kept that side of it quiet," said McClelland.

Now that he's made the decision to close, McClelland says he'll miss everything about L'Espalier, especially the staff.

"The best thing about my career thus far is teaching and seeing the graduates that have worked with me move on and to open up other restaurants, and do great things," said McClelland.

McClelland says he is working on a new project, but declined to say anything else until, he says, the time is right. L'Espalier is holding its final dinner service tonight.