Extra Virgin Olive Oil
2 onions, cut into 1/4-inch dice
2 cloves, garlic smashed and finely chopped
1/2 pound ground beef
1/2 pound ground veal
1/2 pound ground pork
2 tablespoons fresh rosemary, finely chopped
1/2 cup freshly ground Parmigiano
1/4 cup bread crumbs
1 large egg
4 large hamburger buns
4 slices Fontina cheese
2 cups baby arugula
1 large tomato,sliced
1 red onion, thinly sliced
Coat a large saute pan with olive oil, add the onions and bring to medium heat. Season the onions with salt and cook until soft and aromatic, 8-10 minutes. Add the garlic and cook for another 2-3 minutes, stirring frequently. Remove from the heat and let the mixture cool.
In a large bowl, combine the cooled onion mixture with the beef, veal, pork, rosemary, Parmigiano, bread crumbs, egg, and 3-4 tablespoons of water. Mix well and season generously with salt.
Make a 1-2 inch tester patty. In a small saute pan, heat a bit of oil and cook the patty. When it's cool enough, taste it to make sure it's delicious - if it's not, reseason. When the tester tastes fabulous, form the meat mixture into four equal patties.
Preheat a grill or coat a large saute pan with olive oil and bring it to medium-high heat. Cook the burgers 4-5 minutes per side. Toast the buns on the grill or in the toaster. While the second side of the burger cooks, place a slice of cheese on top and let it melt.
Smear each side of the bun lightly with mayonnaise, place a burger on each bottom half, garnish with the arugula, tomato, and onions, top with the other half of the bun, and serve.