From clambakes to weddings to prix fixe, Four Seasons Caterer becomes a restaurant three nights per week.

In between decorating the tables with flowers and tulle for weddings and cleaning up confetti after Sweet 16 parties, owner Jean Mackenzie and her staff are turning the neutral-colored dining room at Four Seasons Caterer in Southampton into a restaurant three nights a week.

The freshly painted white walls, accented by soft overhead lighting, allow the floor-to-ceiling windows across two walls to be the main focal point in the dining room.

“It’s very subtle,” said Ms. Mackenzie standing on the outside porch looking through the open French doors into the dining area.

Just to her left the view from those windows includes a garden with blooming flowers, lawn grass and life-size statues.

Ms. Mackenzie opened the Clamman Seafood Market on North Sea Road in Southampton in 1982 with her late husband, Paul Koster. Over the years patrons asked for everything from cooked lobsters to where to find table rentals for clambakes.

“People started doing weddings on the beach, but they needed a place for the reception,” Ms. Mackenzie said. So in March 2009 she opened Four Seasons Caterer just two blocks away at 15 Prospect Street, the former longtime site of John Duck Jr.’s, being careful to choose a name that conveyed to patrons she was open year-round.

During last summer, Ms. Mackenzie started opening one night per week for dinner at Four Seasons in the historic white house in Southampton and as popularity grew so did the idea for a restaurant more than just once a week.

Serving cuisine is not new to the old home. Before being converted into John Duck Jr.’s by the Westerhoff family, the building was first a farmhouse and then a rooming house.

Now, chef Julio Quisbert, 42, has joined the staff, bringing with him the some of the regional flavorings of his native Bolivia, such as panca pepper in the barbecue sauce. “I’m trying to bring the same infusion for marinades from South America,” said Mr. Quisbert, who worked at Tribeca Grill for seven years as well as in the kitchens of Nobu and Windows on the World atop the World Trade Center.

“We are trying to do a new concept here,” Mr. Quisbert said. “Buffet style and every night prix fixe.” Tuesday night dinner is a choice of either organic barbecue chicken or fish of the day for $39.50; Wednesday night offers a choice of prime rib or steak au poivre for $42.50 and Thursday night the choice is between lobster and barbecue baby back spareribs for $42.50. Guests can also help themselves to the salad bar all three nights.

Guests can also order appetizers ranging from fried Mediterranean calamari served with a marinara red sauce for $8.50 to “home specialty” crab cake with Alaskan crab and black bean and diced avocado timbale for $12.50.

“I decided to make it easy for families,” Ms. Mackenzie said of the prix fixe menu. “Give them plenty to eat and at the same time I integrated the sushi and raw bar.”

Guests can order a $6.50 avocado roll, $7.50 vegetable roll or $9 spicy tuna roll among others off the sushi menu as well as the $9 ceviche special of the day or four jumbo ocean caught wild shrimp with horseradish sauce for $15 off the raw bar menu.

The restaurant also offers a children’s menu.

For now, the restaurant is open Tuesday, Wednesday and Thursday nights starting at 5:30. “We’re just taking baby steps,” Ms. Mackenzie said.