De-stem mushrooms and finely chop the stems.
To a large skillet, over medium-high heat, add chopped mushroom stems, Italian sausage and garlic. Cook until sausage is browned and cooked through. Remove from heat and let cool.
Preheat oven to 350°
In a large mixing bowl, combine cream cheese, ¼ cup Parmesan cheese, and parsley. Mix until well incorporated.
Once the sausage has cooled, add it to the cream cheese mixture. Taste and add salt and pepper if needed.
Spoon heaping mounds of the stuffing mixture into each mushroom cap. Bake on middle rack for 30 minutes.
Sprinkle remaining ¼ cup Parmesan cheese over the top of mushrooms. Broil on high 3-5 minutes, or until Parmesan is a nice golden brown.
Let stand 5-10 minutes before serving.