1 tbsp. olive oil
1 tbsp. butter
2 large onions, chopped
1 large bay leaf
Salt and white pepper
6 slices meaty bacon, halved crosswise
1 ½ lb. ground sirloin
Salt and pepper
8 oz. sharp white cheddar, sliced or coarsely shredded
¾ cup sour cream
¼ cup chopped fresh chives
3 tbsp. Dijon mustard
3 tbsp. prepared horseradish (I like Gold’s)
1 tbsp. Worcestershire sauce
4 brioche burger buns, split
Sliced dill or sweet pickles or cornichons
Upland cress or watercress
Salt and vinegar or dill pickle-flavored potato chips
Arrange the rack in the center of the oven; preheat to 400°.
In a medium skillet, heat the oil, one turn of the pan, over medium. Add the butter. When the butter melts, add the onions and bay leaf. Season with salt and white pepper. Cook, stirring occasionally, until the onions soften (do not brown), 6 to 7 minutes. Stir in 1/2 cup water and cook until evaporated, about 5 minutes. Continue cooking, stirring often, until onions are light golden, about 10 minutes more. Discard the bay leaf.
Line a large rimmed baking sheet with foil and place a wire rack inside the baking sheet. Arrange the bacon on the rack and bake until crispy, 15 to 18 minutes.
While the bacon cooks, heat a large cast-iron skillet or a griddle over medium-high.
Season the ground beef, then form it into 4 patties, thinner in the centers for even cooking. Cook the burgers, turning occasionally, for 6 to 7 minutes, topping with cheese during the last minute or so.
While the burgers cook, in a medium bowl, mix the sour cream, chives, Dijon, horseradish, and Worcestershire; season the sauce.
Build each burger with the bun bottom, onions, pickles, watercress, burger patty, 3 slices of bacon, some sauce, and the bun top. Serve with chips.