Preheat the oven to 400°.

Gently clean the mushrooms to remove any dirt.  Separate the stems from the caps, reserving the stems.  Place the mushroom caps on a small baking sheet.

Heat a small skillet over medium-high heat.  Coarsely chop the mushroom stems.  When preheated, add the butter and allow to melt.  Once melted, add the mushroom stems and sauté for 8 to 10 minutes, until softened and golden around the edges.  Season with salt and pepper and add the garlic, cooking for 30 seconds to 1 minute to soften.

In a small mixing bowl, combine the cream cheese, Parmesan, and cayenne, to taste.  Add the mushroom-garlic mixture and stir to combine.  Season to taste with salt and pepper.  Spoon the filling into the mushroom caps until slightly overflowing.  Sprinkle Parmesan cheese over each mushroom and grind some fresh pepper on top.  Bake for 20 to 25 minutes, until heated through and golden on top.  Allow to cool for at least 5 minutes before serving.  Sprinkle chives on top, if desired.