GRILLED AND smothered in gooey cheese, topped with ketchup and cushioned in a soft, fresh bun, the mighty hamburger rules at Memorial Day backyard barbecues from the Main Line to Manayunk, North Philly to the Northeast.

Any time of year, the hamburger is more popular than pizza or even ice cream in the United States. This weekend alone, we will consume millions of them.

But while we respect the classic burger lineup, we think it's time to gourmet up your game, creating burgers that will amaze your friends and family.

We asked some local restaurant pros for the burger secrets that make absolute addicts out of their customers. What seasonings do they use? What kind of meat? Which breads? Are there secret techniques?

We asked, and we got a mouthful.

It turns out that chefs are very passionate about their burgers, elevating them to gourmet status on their menus with a tweaking of toppings, a special spice or homemade bread.

To begin with, it can't be a good burger unless it starts with the right meat - and most chefs use angus beef that's fresh, never frozen and simply seasoned with pepper and salt. All the chefs we spoke to said that proper fat content in the meat can make or break a burger.

At Goodburger, a newcomer to the city, off Rittenhouse Square at 17th and Chestnut streets, owner Nick Tsoulos prepares all his meat, which he gets from Nebraska and Washington State, to create the perfect fat content, which for him is always 83 percent meat, 17 percent fat.

"It should be to the taste," said Tsoulos, "Not too much fat, but it needs just enough to cook right."

How do you know how much fat is in your meat? If you're buying it at the supermarket, look on the label, which will say 80/20 or 70/30. Better yet, go to a butcher, who will make sure you have the perfect blend.

"The ratio is important," said chef Chad Williams, of Old City's Amada restaurant. "We go to Esposito's [in the Italian market]. Lean meat is not delicious. You want some fat there to keep it moist and juicy."

For other chefs, great meat is key, but so are toppings.

Fork Restaurant owner Ellen Yin won't dream of putting a topping on her burger unless it's in season. So you won't find tomatoes on one of her burger specials if it's not the right time of year.

For Yin, the philosophy makes sense: fresher ingredients mean a tastier burger.

"Almost any topping can work on a burger, but it's better if it's fresh and ripe," said Yin, who is currently topping burgers with Maytag blue cheese and caramelized fennel, or sauteed crimini mushrooms, bacon and avocado.

At Sabrina's Cafe, the Italian Market mainstay that just opened a second location at 18th and Callowhill streets, a burger is definitely about the toppings - lots of them all at once.

Sabrina's/Callowhill chef/owner Lance Silverman puts a different burger on the menu every day, creating a weekly cult following of burger lovers with original combinations that almost seem like a meal on top of a burger.

"People love our burgers," said Silverman. "We give them tons of toppings they can choose from."

We're not talking lettuce, tomato and pickles here.

Silverman uses his imagination to combine things like portabella mushrooms with caramelized onions, or avocado and sauteed spinach or hot peppers with goat cheese.

"The best thing to do is experiment - put together things you really like," said Silverman, who also stuffs a turkey burger with filling (see recipes).

At Iron Hill Brewery, the Brewski Burger, a 10-ounce Angus beef beauty, keeps customers coming back with its combination of roasted mushrooms, smoked bacon and a choice of five cheeses.

The key to making a good backyard burger is having all your ingredients prepared and at the grill before you start, said executive chef Dave Anderson. That means doing a little legwork in the kitchen to prep the toppings, but it will be well worth it. You'll avoid a typical outdoor grill pitfall: burgers that are overdone because the cook has to run inside for forgotten ingredients.

"Before you even turn the grill on, cook the bacon, roast the mushrooms, do whatever you are going to do to get your topping ready," said Anderson.

So you've chosen the best meat and picked out your toppings. You're not done yet.

What good is a burger, say chefs, if it's served on a cruddy, freezer-burned roll? Bread is critical at this juncture.

Most chefs bake their own rolls. Too daunting, you say? Uh, yeah.

So buy fresh rolls at a local bakery the morning of the barbeque, chefs suggest. You can stick with a Kaiser or other soft, round roll - or you can be really bold.

Yin serves her burgers on brioche bread.

"There's nothing like a homemade brioche roll for a burger," said Yin. "You need that - and some crispy fries."*