For burgers:

  • 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

For slaw:

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

Make slaw:

  • 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.