- 1 medium onion, peeled and cut into large chunks
- 12 oz portobello mushroom caps (about 4 large), cleaned, stems trimmed, and cut into large chunks
- 4 thick slices of nitrate-free bacon (optional)
- 2 Tbsp plus 2 tsp bacon fat or olive oil
- 1 lb ground beef or buffalo
- freshly ground black pepper
- sea salt (optional)
- 2 celery ribs
- 1/2 Granny Smith apple, cored but left unpeeled
- 1 1/2 tsp cider vinegar
- 1 tsp olive oil
- 1 tsp whole grain mustard
- 1/4 tsp raw organic honey (optional)
Place bacon on a rack in a shallow pan (jelly roll pan works great). Set oven heat to 400 degrees. Immediately place bacon in oven (before it reaches temperature) until it is about halfway cooked, about 10-15 minutes. Remove from oven and cool slightly. You can also just cook it in a skillet, but baking works best for me.
NOTE: If you don’t have a rack, form crumpled pieces of foil into long strips and create a grid in your pan. Put the bacon on top of the foil grid. Not quite as pretty, but it works. You can also just set the bacon directly on a foil-lined shallow pan. Be sure to pat the bacon grease off the bacon strips before processing it.
While bacon cooks, working in batches, pulse mushrooms and onion in food processor until finely chopped. Remove mixture from processor.
Pulse partially cooked bacon in food processor until finely chopped.
Heat 2 Tbsp bacon fat or olive oil in a large heavy skillet. Add mushroom mixture and bacon, stirring to combine. Add 1/4 tsp pepper.
Cook, stirring occasionally, until vegetables begin to brown and liquid evaporates, 15 – 20 minutes (10 – 15 if not using bacon). Transfer to a large bowl and cool slightly, about 15 minutes.
While vegetables cool, prepare slaw by cutting celery and apple into 2-inch long julienne with a slicer (or by hand). Whisk together remaining ingredients and toss with apples and celery. Let stand 15 minutes (while burgers cook) to develop flavors.
Mix ground meat into cooled mushroom mixture with your hands until well combined. I know, I know…no one wants that stuff under their fingernails, but it’s really the best way to mix. Form into four 4-inch patties.
Wipe out skillet and heat remaining bacon fat or oil. Cook burgers, turning once, for about 8 minutes total for medium rare. I think these burgers would also stand up to outdoor grilling, but I haven’t tried it.
Serve topped with celery apple slaw.