Set out the cream cheese to soften at room temperature. Preheat the oven to 400 degrees F. Grease a baking sheet with a little butter.
Gently rinse the mushrooms in cold water and brush off the dirt (or wipe it off with a damp paper towel). Pat the mushrooms dry and remove the stems by pulling them or cutting them out with a small knife. Place the mushroom caps on the greased pan. Chop up the stems.
Peel and finely chop four cloves of garlic.
In a 12-inch skillet, melt two tablespoons of butter. Add the garlic and cook it for a minute before adding the mushroom stems. Stir to combine and cook the mixture for five minutes or until tender. Remove the stem mixture to a plate and spread it out to cool.
In a medium mixing bowl, add the softened cream cheese and stir it to soften it further. Add ¼ cup mozzarella, ¼ cup Parmesan, two basil leaves cut into ribbons, the lemon zest, pepper, salt, garlic powder and Worcestershire sauce. Add in the mushroom stem mixture. Stir with a spoon to mix well, using a spatula to scrape the spoon and bowl as needed.
Melt four tablespoons of butter in the microwave (place in a microwave-safe bowl and cover with wax paper first) or melt it in a small pan on the stove. Brush some butter all over each mushroom cap, including the insides, tops, bottoms and sides. (You'll have extra melted butter left to pour over the top later.)
Use a small scoop or two teaspoons to scoop some cream cheese filling into each mushroom cap. Try to smooth over the top. Sprinkle the remaining mozzarella on top of the mushroom caps. Pour the remaining melted butter over the mushrooms.
Bake for 15-17 minutes, or until the tops are just starting to get golden.
Top the mushrooms with ribbons of basil and squeeze a little lemon juice over them. Let the mushrooms rest for five minutes before serving.
Store leftovers in the refrigerator for up to five days.
Notes
What to do with extra fillingThis recipe should be enough for 18 mushrooms. If you have extra filling, you can stuff more mushrooms or save the filling to spread on crackers or melt into buttered pasta.Make-Ahead Option:A day ahead, you can brush the caps with melted butter, stuff the mushrooms, but hold off on drizzling melted butter over the top. Refrigerate them without baking. The day you want to serve them, drizzle on melted butter and add five minutes to the baking time. Can you freeze stuffed mushrooms?I haven't tried it, but you should be able to freeze stuffed mushrooms as long as you don't bake them first. I would place them on a wax paper-lined sheet pan in a single layer and freeze for a couple of hours, then transfer them to a freezer bag.Try stuffed mushrooms over buttered pasta! When you cut into a hot mushroom, the filling oozes out into the pasta! You can even stir in extra filling as mentioned above.