Last weekend, Mike McCoy and Derek Stevens flipped 800 beef patties in four hours.

They’ll be back at it again on April 3, making Moonlit Burgers for the masses.

The pop-up burger spot takes over io Deli at 306 Beverly Rd. in Mt. Lebanon every Saturday from 5 to 9 p.m. Order online and grab your meal to go. You might not be able to resist eating it in the car; Moonlit Burgers are out of this world.

The sandwiches are L.A.-style smash burgers made with one or two beef patties from Weiss Provision Company in the Strip District.

It starts as a meatball that’s smashed with a spatula on the griddle, mixed with shaved, sweet onions and cooked until the thin edges are nice and crispy. It’s then topped with two slices of American cheese, homemade spicy pickles and Moon Sauce comprised of gojuchang (a red chili paste), Duke’s mayonnaise, Dijon mustard, Sriracha, pickles and other secret ingredients. All of this deliciousness is served on a Martin’s Potato Roll.

The Double-Full Moon Burger is $8 and a Single-Half Moon Burger is $5. They also make a kid’s version for $5. Complete the meal with Zapp’s Voodoo Chips and a Mexican Coke.

For McCoy and Stevens, who met in 2004 while working at Eleven, Moonlit is a tribute to old-fashioned diner burgers and the West Coast culinary juggernaut In-N-Out Burger.

McCoy, whose parents are from Pittsburgh, grew up in Southern California and is a hardcore fan of the fast-food chain.

“I’ve always thought Pittsburgh was a great burger town with Tessaro’s and all the other places,” he says. “A big part of my family still lives in California and I started seeing these smash burger concepts popping up all over the place. I got to try a few and realized Pittsburghers would be really into what’s going on out there.”

Stevens, a North Hills native, has been in the local restaurant scene for 30 years. He recently had to close his Downtown eatery, Union Standard, due to the pandemic.

For years, the friends have been talking about opening their own spot. When Covid hit, they decided to ditch plans for a brick-and-mortar restaurant and pop up at different locations around town, including Millie’s Homemade Ice Cream in Shadyside and The Vandal in Lawrenceville. Lines wrapped around the block, so they moved to online ordering to provide a safer, more efficient system.

Jeff and Carol Iovino, owners of io Deli and Cafe io, let the pair take over the kitchen when they close at 3 p.m. on Saturdays. In the future, McCoy and Stevens might open their own establishment, but, for now, they’re happy flipping on the fly.

“We want to do a few simple things and have them be enjoyable and at an affordable price point,” Stevens says.