2 normal-sized shallots or in my case, 6 really small shallots, chopped
1 large portobello mushroom cap and half of stem, trimmed and quartered
2 TBSP + 2 tsp olive oil
1 pound ground bison
Celery Apple Slaw:
2 celery ribs
1/2 cored unpeeled apple
1 TBSP mayo
1 1/2 tsp cider vinegar
1 tsp olive oil
1 tsp whole-grain mustard
Accompaniment: 4 English muffins, split and toasted
Equipment: 12-inch heavy skillet
Cook vegetables for burgers:
Finely chop shallots and mushrooms (you can use a food processor or do it by hand). Heat 2 tablespoons oil in skillet over medium heat until it shimmers. Add mushroom mixture, 3/4 teaspoon salt, and 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.
Meanwhile, make slaw:
Cut celery and apple into 2-inch-long thin julienne (either with an adjustable-blade slicer fitted with 1/8-inch julienne blade or by hand with a knife).
Whisk together mayo, vinegar, oil, mustard, 1/8 teaspoon salt, and 1/8 teaspoon pepper in a medium bowl. Add celery and apple, tossing to coat.
Cook burgers:
Mix ground bison into cooled mushroom mixture with hands until well combined. Form into 4 (4-inch) patties.
Heat remaining 2 teaspoons oil in skillet over medium-high heat until it shimmers. Cook burgers approximately 4 minutes on each side for medium-rare.
Top burgers with slaw and serve on English muffins.