Preheat oven to 350 degrees. Line a standard size baking sheet with parchment paper or a silicone baking mat, set aside.
In a large skillet set over medium heat, cook sausage, crumbling as it browns. Using a slotted spoon, transfer sausage to a medium mixing bowl.
Finely chop 6 mushrooms. Add to skillet with the sausage grease and saute until tender, about 3 minutes, then add the onion and garlic. Continue cooking for an additional 3 minutes. Slowly pour in wine to deglaze the pan. Using a whisk, scrape up all of the browned bits off the bottom of the pan. Allow the wine to reduce almost completely. Transfer to the mixing bowl with the sausage.
Add cream cheese, egg yolk, panko, parmesan cheese, salt, garlic, pepper, and 1 tablespoon parsley. Mix to combine.
Spoon mixture into the center of the mushrooms, pressing slightly. Add a little extra to create a mound on top of the mushroom.
Place in the oven and bake for 25 minutes, or until golden brown. Remove from the oven and allow to cool for 5 minutes before sprinkling the tops with the remaining parsley. Serve immediately.