If you’ve heard the name Pat LaFrieda before, you know he’s the city’s foremost meat purveyor. His 100-year-old butcher business has provided some of the most lauded cuts of meat to the city’s fanciest restaurants. The burger blend he created for Danny Meyer’s Shake Shack is the stuff on which business empires are founded.

But as difficult as it might be to believe, this royal of the burger world was a reluctant monarch. In LaFrieda’s new book “Meat: Everything You Need To Know” (Atria Books), it’s revealed that when LaFrieda got the Shake Shack account in 2004, his father (also Pat) was vehemently opposed to making pre-molded patties for a hamburger stand.

“We’re butchers!” the elder LaFrieda cried. “The best burger you can make is by hand.”

But when a 1,200-burger-a-day offer comes, you don’t refuse.

LaFrieda hired a jobless guy from Ecuador, who had been sniffing around his plant for weeks looking for work, to form the patties by hand every day. (“Ecua,” as he’s known, still works for LaFrieda. But there’s a machine that now makes the molds.)

Since then, 1,200 has grown to, at last count, 50,000. But even before then, LaFrieda had been the undisputed gold standard in New York butchery, getting his own billing on menus.

“Henry Meer came up to me in 1998 . . . and asked if I could make a custom blend just for him,” LaFrieda tells The Post. “He was opening the restaurant City Hall in Tribeca, and he wanted to serve a really great burger. Henry wanted his burger to have a bit more fat and to be a little sweeter, and I was happy to provide him with it. It was the first custom blend I made, and Henry was the first to put our name on his menu — it read, ‘Pat LaFrieda’s custom blend of short rib and brisket.’ ”

His book tells the story of the business LaFrieda inherited from his father on Leroy Street (which moved to New Jersey a few years ago), as well as a handy guide to the art of butchery. LaFrieda explains everything from the butcher’s tool box (did you know, for instance, that for a smooth cut of steak you should use a scimitar?), to breaking down a calf, to Grandma LaFrieda’s recipe for braised stuffed veal.

Given that Labor Day is everybody’s favorite excuse to break out the gas grill and the Lipitor and indulge our most primal meat fantasies, we asked LaFrieda for his tips — and recipes — for achieving hamburger nirvana.

Smash Burger

“A smash burger is a burger where the patty is formed tall, or even round, then smashed down while it’s on a griddle,” writes LaFrieda. “The idea is that while you’re smashing the patty, you’re also helping to get a nice char on the outside. A smash burger is typically made with a 4-ounce patty. I am an 8-ounce meat guy, so I always order doubles.”

To make a double smash burger: ”Form two (4-ounce) balls of chopped beef and season them with kosher salt and freshly ground black pepper. Put the balls in a very hot skillet or on a griddle. While they’re cooking, smash the balls to ¾ of an inch thick. Have a Martin’s Potato Roll handy. Cook the patties about three minutes per side for medium-rare. Stack the patties on the buns, and dress them how you like.”

LaFrieda says Schnippers (620 Eighth Ave.) does a “great job” with smash burgers.

Bill’s Burgers’ Double Beef Sliders

“The most common mistake when making sliders,” explains LaFrieda, “is the ratio of meat to bread: The bun is too big, and the patty is too small. A perfect slider has a 3-ounce patty,” but most are about 2 ounces, he says.

“What Bill’s does differently is that they make one long rectangular patty. They serve the sliders with three buns in a row, right next to each other, with one long patty lying on top. It looks like three separate sliders, but you soon find out you have to cut between each bun to divide the patty. This way you can cook them on the grill without them falling through the grates, and if you’re cooking a bunch, you have fewer to flip. Their rectangular patty makes three 1 ¹/₂ -ounce sliders — too small for me — so I always order mine double. I’m going to get my 3-ounce slider one way or another.”

How to make it

1. For the onions: In a large skillet, heat the olive oil over medium-low heat until the oil slides easily in the pan, about 2 minutes. Add the onions and cook, stirring occasionally, until they are very soft, about 20 minutes. Season with salt and pepper and continue cooking until they are deeply browned and caramelized but not burned, about 10 minutes. Remove from heat.

2. Preheat the broiler or preheat a grill for toasting the buns.

3. To make the sliders, divide the meat into eight (4 ¹/₂-ounce) portions. Form each portion into a rectangular patty about 5-by-2 inches and ¹/₂- inch thick. Season the patties on both sides with the salt and pepper.

4. On a griddle or in a large skillet, heat the canola oil over medium heat. Place the patties in the pan, making sure not to overcrowd it (you can fit four in a large skillet, more on a griddle), and cook for 1 minute without moving them so they crisp up on the outside. Flip the patties, lay three cheese slices across four of the patties, and cook the other side until crisp, about 1 minute more for a medium-rare slider.

5. While the sliders are cooking, break the buns into rows of three and open them up. Brush the cut sides of the buns lightly with the melted butter and broil or grill to toast them lightly, 1 to 2 minutes. Spread the buns with ketchup and mustard and lay three or four pickle slices across the buns.

6. Take the plain slider patties out of the pan or off the grill and lay them on the buns, and lay one cheese-topped slider patty on top of each plain patty. Top each set with about 3 tablespoons of the caramelized onions, put the tops of the buns on, and serve. Makes 12 double sliders.

Copyright © 2014 by Pat LaFrieda from MEAT: EVERYTHING YOU NEED TO KNOW published by Atria Books, a division of Simon & Schuster, Inc