Make the filling. Heat a skillet over medium heat and add the sausage. Cook for 5-7 minutes, using a spoon to break the sausage into small pieces, until browned and mostly cooked through. Add in the chopped mushroom stems, garlic, sage leaves, Italian seasoning, and salt and cook for 2-3 additional minutes until the mushrooms are softened. Stir in the dairy free cream cheese until melted.