Step 1

Place a rack in the center of the oven. Preheat the oven to 350 degrees F. With a paper towel, wipe off the outsides of mushrooms. Remove and finely chop the stems. Set the caps aside.

Step 2

Heat the oil in a large nonstick skillet over medium. Brown the sausage until cooked through, using a sturdy spoon to break apart the meat into small pieces (sausage is kind of a pain to break into small pieces—once I have the pieces fairly small, sometimes I use a potato masher to split them further). This will take about 8 minutes.

Step 3

To the skillet, add the mushroom stems, vinegar, salt, and pepper. Cook until the stems are softened, about 4 minutes.

Step 4

Stir in the green onion, garlic, and Italian breadcrumbs. Set aside to cool.

Step 5

In a large bowl, stir together the cream cheese, egg yolk, and Parmesan with a fork until smoothly combined.

Step 6

Fold in the sausage mixture.

Step 7

With a spoon, generously fill each mushroom cap so that you create a mound on top. Arrange in a baking dish large enough to hold them snugly in a single layer (they will touch at the edges).

Step 8

Bake the stuffed mushrooms until browned and the filling is cooked through, about 20 minutes. Some liquid may seep out; simply leave it behind in the pan.

Step 9

Transfer to a serving plate and let cool at least 5 minutes. Sprinkle with fresh parsley. Enjoy warm or at room temperature.