- 1 tablespoon olive oil
- 1/2 small red onion, finely chopped
- 1 cup ketchup
- 1 cup Medjool dates, pitted, chopped
- 1/2 cup pale lager
- 2 tablespoons apple cider vinegar
- Kosher salt, freshly ground pepper
- 1/2 small red onion, finely chopped
- 2 garlic cloves, finely chopped
- 1 pound ground lamb
- 8 ounces ground beef
- 1/4 cup finely chopped fresh flat-leaf parsley
- 1 tablespoon baharat (spice blend)
- Kosher salt, freshly ground pepper
- 1 tablespoon vegetable oil
- 12 slider buns, split, toasted
- Bibb lettuce, caramelized onions, and sliced feta (for serving)
- Baharat is available at Middle Eastern markets and online.
- Heat oil in a small saucepan over medium heat. Cook onion, stirring occasionally, until beginning to brown, 5–8 minutes. Add ketchup, dates, and beer; bring to a boil, reduce heat, and simmer, stirring occasionally and adding water as needed to prevent burning, until thick and slightly darkened, 20–25 minutes.
- Remove pan from heat and stir in vinegar. Let mixture cool slightly. Purée in a blender, thinning with water if needed, until smooth; season with salt and pepper. Let cool.
- DO AHEAD: Date ketchup can be made 5 days ahead. Cover and chill.
- Using your hands, gently mix onion, garlic, lamb, beef, parsley, and baharat in a large bowl; season with salt and pepper. Form scant 1/4-cupfuls of lamb mixture into twelve 2″-diameter patties.
- Heat oil in a large skillet over mediumhigh heat. Place patties in skillet and immediately reduce heat to medium. Cook about 3 minutes per side for medium-rare. Serve patties on buns with date ketchup, lettuce, caramelized onions, and feta.