- 1 medium onion, chopped
- 10 ounces portobello mushrooms, trimmed and quartered
- 2 tablespoons plus 2 teaspoons olive oil, divided
- 1 pound ground beef
- 4 toasted buns
2 celery ribs
1/2 Granny Smith apple, cored (left unpeeled)
1 tablespoons mayonnaise
1 1/2 teaspoons cider vinegar
1 teaspoon olive oil
1 teaspoon whole-grain mustard
Rounded 1/4 teaspoon sugar
- Cook vegetables for burgers:
- Pulse onion and mushrooms in a food processor until finely chopped.
- Heat 2 tablespoons oil in a 10-inch heavy skillet over medium heat until it shimmers.
- Add mushroom mixture,
- 3/4 teaspoon salt, and rounded 1/4 teaspoon pepper and cook, stirring occasionally, until vegetables begin to brown and liquid has evaporated, 8 to 10 minutes.
- Transfer to a bowl and cool to warm, stirring occasionally, about 15 minutes
- Cut celery and apple into 2-inch-long thin julienne with slicer. Whisk together mayonnaise, vinegar, oil, mustard, sugar, rounded 1/8 teaspoon salt, and 1/8 teaspoon pepper in a medium bowl. Add celery and apple, tossing to coat. Let stand 15 minutes to develop flavors.
- Finish and cook burgers:
- Mix meat into cooled mushroom mixture with your hands until well combined. Form into 4 (4-inch) patties. Grill on your BBQ
- Serve burgers, topped with slaw, on buns.