- 6 blue potatoes, peeled and quartered
- Salt and pepper
- 1/2 cup crumbled stilton cheese
- 1/2 cup heavy cream
- 1/4 cup finely chopped chives
- 2 pounds ground beef sirloin
- 1/4 cup Worcestershire sauce
- 4 cloves garlic, grated
- 1/4 cup grated onion with juice, plus 1 onion, thinly sliced
- 1/4 cup chopped flat-leaf parsley
- Extra-virgin olive oil (EVOO), for drizzling
- 2 tablespoons butter
- 3/4 pound cremini mushrooms, sliced
- 4 cups packed watercress leaves
In a large pot, add the potatoes and enough water to cover. Bring to a boil, add salt and cook until tender, 15 minutes. Drain, return to the pot and mash with the cheese, cream and chives; season with salt and pepper.
Meanwhile, in a bowl, combine the beef, Worcestershire, garlic, grated onion, parsley, salt and pepper. Form 4 large patties. Drizzle with EVOO.
Preheat a cast-iron skillet over medium-high heat. Add the beef patties and cook, turning once, for 10 minutes for medium-rare.
While the burgers are cooking, heat a medium skillet over medium heat; add the butter. Add the sliced onion and cook until softened, 8 to 10 minutes. Add the mushrooms and cook until softened, 8 to 10 minutes more. Season with salt and pepper.
Divide the watercress and patties among 4 plates; top with the onion-mushroom mixture. Serve with the potatoes.