White Truffle Burger with Sweet Caramelized Onions, Gruyere, and Sherry Mayonnaise

Truffle oil is one of my favorite ingredients and I am always looking for new ways to use it.A burger with truffle oil seemed like a natural fit.

Ingredients:

Sherry Mayonnaise
1 cup Mayonnaise
1 clove of garlic, minced
1 tablespoon dry sherry
1 tablespoon fresh rosemary, finely chopped
1/4 teaspoon sea salt

Sweet Caramelized Onions
2 tablespoons extra virgin olive oil
2 tablespoons butter
4 large onions, thinly sliced
1 teaspoon sugar
1/2 teaspoon sea salt

Patties
1 tablespoon extra virgin olive oil
1 tablespoon butter
6 mushroom caps, minced (preferably baby bella mushrooms)
2 garlic cloves minced
2/3 cup of flat leaf parsley, finely chopped
2 lbs ground beef chuck
2 tablespoons white truffle oil (olive oil based)
2 1/2 teaspoons sea salt
1 teaspoon fresh ground black pepper

Vegetable oil, for brushing on the grill rack
6 oz of Gruyere cheese sliced into 6 1oz slices
6 brioche rolls
3 tablespoons white truffle oil (olive oil based)

Instructions:

Prepare a medium-hot fire in a charcoal grill with a cover, or preheat a gas grill to medium-high.

To make mayonnaise, combine all ingredients in a bowl and whisk to blend well. Cover and refrigerate until assembling the burgers.

To make onions, heat the extra virgin olive oil and butter in a fireproof skillet. Add the onions and cook for 10 minutes until the onions are translucent. Add the sugar and salt to the onions and saute until caramelized, about 15-20 minutes. Remove onions from heat, cover skillet and set aside.

To make the patties heat the extra virgin olive oil and butter in a fireproof skillet. Add the mushrooms and garlic and saute until the mushrooms are soft, about 5-10 minutes. Remove the skillet from the heat, add the parsley and allow to cool for 5 minutes. Combined the ground chuck, truffle oil, salt and pepper, and mushroom mixture in a large bowl. Mix well with a fork as little as possible to avoid compacting the beef. Form into 6 equal patties to fit the rolls and depress the centers for even cooking.

Brush the grill rack with the vegetable oil. Place the patties on the rack, cover and cook, turning once, until done to preference, about 3-5 minutes on each side for medium. During the last minute of cooking place 1 oz of the Gruyere on each patty, cover, and allow to melt. Remove the patties from the grill, brush both sides of each roll with the truffle oil, place on the rack and toast until golden brown.

To assemble the burgers spread the toasted side of each roll with the mayonnaise. Place each burger on the bottom side of a roll, divide the onion mixture equally amongst the 6 burgers. Add the roll tops and serve!