Burger Patties 

1. In a large sauté skillet melt 3 Tbsp of unsalted butter. Add the onions, mushrooms and garlic and cook over medium heat stirring. When mushrooms begin to release their moisture, turn the heat to low and cook, stirring occasionally, until the liquid has evaporated and the mixture look dry, 20 to 25 minutes. Season to taste with sea salt and black pepper. Let cool.
2. In a large mixing bowl combine the half of the mushroom duxelles to the rest of the ingredients and gently mix. Portion mix into 6 oz burger like patties.  Set aside.
3. In a small mixing bowl combine about 3 cups of finely shredded romaine lettuce with white truffle oil, fresh lemon juice and season to taste with sea salt. Keep cold until needed. Should be made fresh.
4.  Cook the patties in a hot grill or a skillet to 165*F internal temperature on low to medium heat. Do not squeeze the patties because the moisture will come out and your patties will turn dry. Melt the slices of gruyere cheese and lightly toast the buns.
5. Assemble burgers starting by applying light mustard on the bun, then the lettuce, patty and lastly the mushroom duxelles. Cut in half for easy eating.