The coming of Shake Shack to Harvard Square has plenty of people excited, but the first flavor offered by the celebrated East Coast burger chain isn’t a burger. Or fries. Or a shake. It’s chocolate – hot chocolate.

The site at 92 Winthrop St, once the Om restaurant and nightclub, will likely open by the end of the year with renovations that began in October. It’ll be the second Massachusetts location after Chestnut Hill, which opened in March, and seat 108, according to The Harvard Crimson.

First, though, the Harvard Square Business Association says Shake Shack is saying hello by offering visitors free dark hot chocolate from 1 to 4 p.m. Saturday.

“Shake Shack’s house-made hot chocolate features a blend of bittersweet dark chocolates, fresh milk and cream,” the association says.

The Charles Hotel says the same hot chocolate – as well as the restaurant’s frozen custard – will be handed out at its Sunday ice skating rink opening, which takes place from noon to 6 p.m. Sunday at 1 Bennett St.

For those unfamiliar with the chain, it describes itself as “a modern-day ‘roadside’ burger stand serving the most delicious burgers, fries, hot dogs, frozen custard, beer, wine and more” since launching from a cart set up in a New York park between 2001-03.

Shake Shack’s chief executive, Randy Garutti, told the Crimson that the chain’s customer experience and food quality sets it apart from other burger restaurants. “Shake Shack has always been about taking what fast food ruined over the last 60 years and resetting the conversation on that,” he told the Crimson. “People don’t know what to call us because it’s not fast food, it’s more fine-fast or fine-casual.”