½ pound sliced bacon, cut into ½ inch pieces
1 ½ cup chopped yellow onions
1 pound of button mushrooms, thinly sliced
1 teaspoons salt
½ cup minced shallots
2 sprigs fresh thyme or ½ teaspoon dried
1 sprig fresh rosemary leaves or ½ teaspoon dried
½ cup dry red wine
2 tablespoons flour
2 cups rich beef stock
½ cup heavy cream, plus 2 tablespoons
2 ½ pounds ground beef, such as ground chuck
2 egg yolks
2 teaspoons dijon mustard
1 ½ teaspoons worcestershire sauce
1 tablespoon minced garlic
freshly ground black pepper
2 tablespoons cold unsalted butter
2 tablespoons chopped chives
In a large skillet over medium heat, cook the bacon until most of the fat is rendered but it is not yet crisp. Transfer the bacon to the bowl of a food processor and set aside. Remove all but 3 tablespoons of the bacon fat from the skillet. Reserve the additional rendered bacon fat in a small bowl.
Add the chopped onions to the fat in the pan and cook, stirring occasionally, until very soft and caramelized around the edges, about 6 minutes. Combine the onions with the bacon in the bowl of the food processor and process until smooth. Transfer to a large bowl and let cool.
Heat 3 tablespoons of the bacon fat in the pan. Add the mushrooms and 1 teaspoon of the salt and cook, stirring occasionally, until they have released their liquid and are golden brown around the edges, about 5 minutes. Add the minced shallots, thyme, and rosemary and cook until the shallots are soft (about 2 minutes). Add the red wine and cook until almost completely evaporated. Sprinkle the flour over the shallots and mushrooms and stir to combine. Cook for about 1 minute and add the beef stock. Cook for 5 minutes until thickened. Add ½ cup of the heavy cream, stir to combine, and cook until the sauce is thick enough to coat the back of a spoon and the flavors come together (about 6 minutes). Cover and keep warm while you prepare the steaks.
Preheat broiler or charcoal grill to 500 degrees F.
In the mixing bowl with the pureed onion-bacon mixture, add the beef, the remaining 2 tablespoons of heavy cream, egg yolks, mustard, Worcestershire sauce, garlic, some black pepper to preference, and mix lightly but thoroughly.
Shape the mixture into 6 – 8 oval patties, about 1 cup each, and 1 – 1 ½ inch thick, and transfer to a nonstick baking sheet or broiling pan. If using a charcoal grill, just place the patties directly on the grill surface. Broil or grill the patties close to the heat source, about 4 minutes on each side for medium-rare.
Add the butter and chives (and if using the broiler, the meat pan drippings) to the sauce and stir until the butter is thoroughly incorporated. Taste and adjust the seasoning if necessary.
Serve the patties immediately with roasted garlic mashed potatoes with some of the mushroom sauce on the top.