The first time Kevin Doherty tried to make a 500-pound pumpkin pie for TD Garden’s annual Table of Friends event, a gathering at the arena that feeds many of the city’s homeless for the Thanksgiving holiday, he only had a few days’ notice.

The idea arose four years ago on a whim from the company’s president, Amy Latimer, the executive chef said. And while Doherty, who’s no stranger to whipping up large batches of food, was at first stumped about how to concoct such a massive dessert, he gladly accepted the challenge.

“You don’t tell the president no,’’ he said. “You figure it out.’’

With little time to spare, Doherty had carpenters at TD Garden build him a giant cake mold. Then he had to come up with a way to make the crust. His first idea? Rice Krispies Treats.

“That was an epic fail,’’ he said. “You know what happens to a Rice Krispies Treat when it gets cold? It turns into cement.’’

These days, Doherty has the process of putting together a pie big enough to feed more than 1,000 guests down to a science. In the coming weeks, he will once again set to work with nearly a dozen helpers in the kitchen to prepare a mammoth dessert for Table of Friends, which is now in its 22nd year.

“It’s almost a fun process now,’’ he said.

Doherty uses the same cake mold that was built for his first 500-pound pie, but instead of Rice Krispies Treats, he’s turned to graham cracker crumbs — between 75 and 90 pounds’ worth, mixed with butter — for the crust.

Once that layer is set into place on top of baking sheets, the kitchen staff fills the mold, which is about the size of a table you’d sit at during a wedding reception, with gallon upon gallon of pumpkin pie filling.

Because there isn’t an oven large enough to fit the pie and cook it, Doherty makes a filling that is more like “a pumpkin-mousse-Jello-cheesecake,’’ and then stuffs it into a big refrigerator at TD Garden until it’s time to slice and serve it.

In all, it takes 145 cans of traditional canned pumpkin; 60 to 80 pounds of brown sugar; 3 pounds of cinnamon; 6 pounds of pumpkin pie spice; less than a pound each of nutmeg, allspice, and mace; 6 gallons of gelatin; and around 3 gallons of melted butter to get the job done.

On the day of the feast, Latimer, TD Garden’s president, will use a customized tool to cut the pie. It’s then served up in small portions to the many guests.

Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear.