The stuffing of in these mushrooms is SO tasty you could almost serve it by itself!
8 large green olives, pitted
1/4 cup pine nuts lightly toasted
2 handfuls fresh flat-leaf parsley
2 garlic cloves
1 pound Italian sausage, removed from casing
3/4 cup freshly grated Pecorino Romano
Extra-virgin olive oil
Kosher salt and freshly ground black pepper
Pinch red pepper flakes
1 cup fresh bread crumbs, dried out
24 large white mushrooms, stems removed
Preheat oven to 400 degrees F.
To make the stuffing, put the olives, pine nuts, parsley, and garlic on a cutting board and chop, and put into a mixing bowl. Add the sausage and 1/2 cup of the cheese. Drizzle the stuffing with about 1/4 cup of olive oil to moisten and season with salt, pepper, and red pepper flakes; mix well with your hands to combine. Put the bread crumbs in another bowl, drizzle with a bit of olive oil and add 1/4 cup of the Pecorino; season with salt and pepper.
Oil the bottom and sides of a casserole dish which is large enough to hold all the mushrooms in a single layer. Arrange the mushrooms snugly in the pan, cap side down; season the insides with salt and pepper and drizzle with olive oil. Stuff each mushroom with a generous spoonful of the sausage stuffing and sprinkle the bread crumbs on top; drizzle with even more oil. Bake for 20 minutes until the stuffing is browned and the mushrooms soft, rotating the dish periodically for even cooking.