Preheat the oven to 400ºF / 200ºC degrees and line a baking sheet with parchment paper.
Remove the stems from each mushroom and lay the caps onto the lined baking sheet. Chop the stems finely.
Melt the butter in a skillet and add the chopped mushroom stems and cook until softened and they have released all their water. Season with salt and pepper.
Add in the panko breadcrumbs and cook until they have toasted. Allow to cool a little.
Bake the mushroom caps for 10–15 minutes in the oven whilst you prepare the rest of the filling.
Place the mushroom and breadcrumbs mixture into a bowl and add in the cream cheese, parmesan, parsley and thyme and season with a little more salt and pepper if required.
Remove the caps from the oven and fill with the filling. Top with a little additional parmesan then place back in the oven for around 15–20 minutes until golden and bubbling.
Serve on a platter with a final sprinkling of parsley.