Remove stems from mushroom, slice off the hard end & discard & finely chop the rest and set aside. With a spoon or melon baller, carefully clean out the insides of the mushrooms and discard gills. Take a small slice off the top of each mushroom so it will stand up nicely without wobbling when turned over to be filled.

Add oil to a small skillet, add the sausage, the chopped mushroom stems, apple and, onion, cooking until vegetables are tender and sausage is brown. Add the apple cider and the apple cider vinegar or brandy and continue to cook until nearly evaporated. The bottom of the skillet should look just a bit wet but there should be no pooling liquid.

Turn off heat and lightly mix in parsley and breadcrumbs, season generously to taste with salt and lots of black pepper, keeping in mind that the seasoning is going to flavor the mushrooms as well. If the mixture seems too sweet, add a little more vinegar or brandy.

Mixture should not be wet, but breadcrumbs should look moist. Drizzle with a touch more cider if needed.

Scoop or spoon a scant teaspoon to a tablespoon of the stuffing, depending on the size of the mushroom, into each mushroom, mounding the mixture up.  Place on a parchment-lined rimmed baking sheet. May be made several hours ahead and refrigerated, covered.

Preheat oven to 350 degrees. Drizzle very lightly with a touch of olive oil, if desired. Bake until tender, about 25 minutes.

Notes:

• On cheese: If desired mix a little cheese into the breadcrumbs.
• May be made ahead.