The Dish: Viral BLT sandwich from Middle Child in Center City Philadelphia

PHILADELPHIA (WPVI) -- If you're a Philly foodie, then you know that we have five seasons and the one we're in right now is Middle Child's BLT season.

The viral sandwich just made its debut at the Center City sandwich shop, now that the heirloom tomatoes are ripe and ready to go.

I weaved through the massive line to get the secrets to their best seller.

"I feel very lucky," says Middle Child owner Matthew Cahn, as we look out at the hundreds of people waiting in line outside the shop at 11th Street between Spruce and Locust streets.

His sandwich stacking team is hustling, making a BLT a minute.

BLT season at Middle Child is only available from around mid-July until late August.

"We have to be malleable," says Cahn. "We don't know until we know."

The stars of his best seller are grown at Urban Roots Farm in Newtown Square.

"We just wait and we wait, and then one day they pick up the tomato phone say: 'Matt, they're ready to go. And I say, 'Okay, everybody go!'," says Cahn.

The faithful know it's worth the wait because the heirloom's moment is fleeting.

"Last year, the season was about four or four and a half weeks, and we sold somewhere between 18,000 and 19,000 sandwiches," says Cahn.

He opened Middle Child in 2017.

"I'm the middle child, of course," he says. "I just needed someone to notice me. I was like, I'm gonna make some sandwiches until they notice me. I guess it worked."

Boy, did it! Cahn's sandwiches are critically acclaimed.

Back in 2023, his pastrami egg and cheese sandwich won him the trophy for Good Morning America's Ultimate Breakfast Spot.

Cahn has a sit-down, more dinner focused location in Fishtown called Middle Child Clubhouse, and a spot at Philadelphia International Airport.

"We're also in the Chase Lounge, also at the airport," he says.

Here are the secrets to his sandwich.

First, the tomatoes. They must be heirloom and they must be juicy.

Next, the bread. He went with the classic rye.

"We use a local rye bread made for us by Merzbacher's Bakery out in Germantown," he says. "Nice and toasted. We like it to be like a little bit on the crispier side for this particular sandwich, because it's a sloppy, juicy mess. And then we're gonna hit it with a lot of mayo. We like to go like kind of edge to edge, make sure it gets full coverage."

If you were wondering, he only uses Duke's.

Next, add nice, crispy bacon.

"We put a lot on it," says Cahn. "Five slices for every sandwich."

He adds three or four tomato slice, stop light style: a red, a yellow and a green heirloom.

They make their own tomato vinaigrette and use it to dress the arugula he stacks into the sandwich.

"We like arugula for this," he says. "It's just a little bit more peppery, a little bit more lively."

He also has a BBLT on the menu. The second B stands for burrata and that calls for sturdier bread, so they use ciabatta.

This sandwich also has a tomato chili jam.

"This is spicy and sweet," he says.

How long the BLT season lasts at Middle Child is anyone's guess.

Better get it while it lasts!