• Prep Mushrooms: Clean mushrooms by wiping with a damp paper towel or a mushroom brush. Using your hands, remove stems and set aside (don’t discard stems).
• Marinate Mushroom Caps: Transfer mushroom caps to a large mixing bowl and toss with vinegar and oil. Set aside to marinate for 10-15 minutes.
• Preheat Oven: Preheat oven to 375 degrees F (190 degrees C). Pull out and set aside a 9x13-inch baking pan.
• Cook Sausage: To a large skillet over medium heat, add ground sausage and cook until it’s browned and cooked through and reaches 160 degrees F internally, breaking into small pieces as it cooks. This usually takes 5-7 minutes.
• Chop Mushroom Stems: While sausage is cooking, finely chop mushroom stems.
• Remove Excess Grease: Remove skillet from heat and use a paper towel to blot away any excess grease from the sausage. Alternatively, transfer sausage to a paper towel-lined plate.
• Prepare Sausage Filling: To a mixing bowl, add cooked sausage, chopped mushroom stems, softened cream cheese, breadcrumbs, Parmesan cheese, minced garlic, parsley, salt, and pepper. Mix everything until it reaches the consistency of a stuffing.
• Stuff Mushrooms: Take each marinated mushroom cap and use a small spoon to stuff them generously with sausage mixture, pressing it in gently, to form a small mound. Then, transfer each stuffed mushroom to your baking pan.
• Bake Stuffed Mushrooms: Transfer baking pan to the oven and bake for about 20-25 minutes, or until mushrooms are tender and the stuffing is golden brown on top.
• Serve: Remove baking pan from the oven and let mushrooms cool for a few minutes before serving on a serving platter.

TO PREPARE IN ADVANCE:

• Clean Mushrooms (1-2 Days in Advance): Clean and remove the stems from the mushrooms. Finely chop the stems and refrigerate them in a separate covered container for the filling. Store the cleaned mushroom caps in a paper towel-lined container or a plastic bag and refrigerate.
• Prepare Filling (1 Day in Advance): Cook sausage, then mix it with the chopped mushroom stems, cream cheese, breadcrumbs, Parmesan cheese, minced garlic, parsley, salt, and pepper. Once mixed, transfer filling to an airtight container and refrigerate.
• Stuff Mushrooms (Day Of): Take prepared filling and cleaned mushroom caps out of the refrigerator, then marinate for 10-15 minutes in vinegar and oil. Stuff the marinated mushrooms with filling.
• Bake (Day Of): Preheat oven to 375 degrees F (190 degrees C) and bake the stuffed mushrooms as instructed (see Step #9 above). You may need to add a few extra minutes to the baking time to account for the cold filling and mushrooms.