Ingredients:

•  1 1/4 pounds ground chuck

• 1 teaspoons kosher salt

• 1/2 teaspoons black pepper

• salt and black pepper to taste

• 2 teaspoons extra-virgin olive oil, plus more for brushing

• 1 small red onion, halved and thinly sliced

• 1 8 ounce package sliced mushrooms

• 1 tablespoon Worcestershire sauce

• 1/4 cup ketchup

• 2 teaspoons dijon mustard

• 4 thin slices gruyere (could use havarti as well) cheese

• 4 sesame buns

• Boston or Bibb lettuce

• (Optional) Potato Chips or pickles

Directions:

1. Preheat the broiler and line the bottom of a broiler pan with foil. Lightly mix the beef with 1 teaspoon salt and 1/2 teaspoon pepper in a large bowl. Gently form into 4 patties, about 3/4 inch thick. Arrange on the prepared pan and brush both sides with olive oil. Broil until browned, about 4 minutes per side for medium rare. Cook longer depending on how you like your burger cooked.

2. Meanwhile, heat 2 teaspoons olive oil in a large skillet over medium-high heat. Add the onion and cook, stirring, 2 minutes. Add the mushrooms and cook 2 more minutes. Add the Worcestershire sauce and stir for about a minute. Season with salt and pepper and remove from the heat. Combine the ketchup and mustard in a separate small bowl and set aside. 

3. Top each patty with one-quarter of the mushroom mixture and 1 slice cheese. Return to the broiler to melt the cheese, about 30 seconds.

4. Spread the buns with the ketchup mixture; top with some lettuce. Serve with chips and/or pickles.