This delicious recipe for sliders is courtesy of Riad Nasr and Lee Hanson of Minetta Tavern.
Season beef with salt and pepper. Form into three equal-size patties; set aside.
In a large skillet, heat butter over medium-high heat, add onions. Cook, stirring occasionally, until caramelized, about 10 minutes.
In a cast-iron skillet, heat oil over medium-high heat. Add beef patties and cook about 1 1/2 minutes for medium-rare.
Place patties between brioche halves; top with onions. Serve immediately with pickles, if desired.