In the centre of the puff pastry square, pour the entire creamy truffle mixture. Spread it across the middle of the pastry, leaving about a 10cm wide gap on the top, bottom and sides. This 'empty frame' will help you fold the galette into a perfect square.
Once you have finished spreading the mixture in the middle of the pastry, fold the 10cm wide gap along the edges of the square mixture, wrapping the sides over the filling. Secure the corners by gently pressing it down with your bare fingers.
Using a brush and a bowl of 1 whisked egg, gently brush the edges of the pastry with the egg wash for a shiny glaze.
You can dust the toasted pine nuts around the edges of the pastry before and after baking for that extra crumble.
Bake the galette on 175 degrees Celsius for 30 minutes. Serve hot