Heat oven to 180c
Pull the stalls out of the mushrooms ( keep them to add to another dish )
Brush the mushrooms with kitchen towel to remove any dirt . Do NOT wash them
Put in an oven proof dish , gills facing up
Put the garlic slices in the gills , scatter over the thyme , dot with butter .
Season with salt and pepper
Bake for about 15-20 minutes
Serve