Preheat the oven to 190°C. Brush a 20cm x 2cm loose-bottomed tart pan with a little butter. Use a fork to mash cheeses, thyme, creme fraiche and egg. Season with salt and pepper.
Place a filo square in base of tart pan, letting excess hang over sides, and brush with butter. Repeat until all pastry is used. Place filling in centre, spreading well. Scrunch up excess pastry and brush scrunched pastry with remaining butter. Place on a baking tray and bake for 25 minutes or until golden. Set aside for 5 minutes to rest, then remove from pan.