• Preheat oven to 400℉. Line a baking sheet with parchment and set aside.

Make the Mushrooms and Filling:

• Remove the stems from the mushrooms. Finely mince the mushroom stems and set aside. Add the mushroom caps to the prepared baking sheet, drizzle with 2 tablespoons of olive oil, and toss to coat. Set aside.
• In a large skillet over medium heat, add 1 tablespoon of olive oil. Once hot, add the Italian sausage, breaking it up into small pieces and cooking until browned and crisp, about 5-7 minutes. Once the sausage is fully cooked though, use a slotted spoon, and transfer the sausage to a medium mixing bowl.
• To the same skillet, add the remaining tablespoon of olive oil, shallot, and chopped mushroom stems. Stir the mixture to coat the mushroom stems and shallot in the oils, and spread into an even layer. Allow the mushroom stems to sear and get golden brown, about 3 minutes before stirring.
• Continue to cook until most of the liquid from the mushrooms has cooked out and the shallots are translucent, about 1 more minute. Add in the garlic, white part of the scallions, dried sage, salt, and pepper. Sauté until the garlic is fragrant and the spices smell toasted, about 1 minute. Pour in the sherry vinegar, deglazing the pan and stir to combine. Transfer the contents of the skillet into the medium bowl with the sausage.
• To the bowl, add the green parts of the scallions, softened cream cheese, parmesan, parsley, fresh thyme leaves, lemon zest, panko breadcrumbs. Stir until the filling is combined. Set aside.

For the Panko Topping:

• In a separate mixing bowl, add the panko breadcrumbs, olive oil, kosher salt, parmesan, parsley, and paprika. Toss together to combine.

To Assemble:

• To each mushroom, add about 1 heaping tablespoon of filling, pressing the stuffing into the well of the mushroom cap, ensuring it is tightly packed and forming a dome. It’s okay if they look a little overstuffed! Turn the stuffed mushroom upside down, and gently press the stuffing into the panko topping, rotating it around so it is totally covered, ensuring the topping it is pressed well into the filling so that it sticks. Transfer to the sheet pan, stuffing side up, and repeat.
• Transfer the sheet pan to the oven and bake for 35 minutes until the mushrooms are a rich brown and the stuffing is crispy and golden. Allow to cool slightly before serving.