Add the sugar, butter and milk to a medium sized pan and using a whisk, mix the ingredients together as they melt. When it has achieved a rolling boil, continue to whisk for a further two minutes, then remove from the heat.
Add the pecans and allow to cool for a bit.
Roll out your pastry dough on a sheet of baking paper (you want the pastry fairly thin). Don't worry about an exact shape, but cut off any longer sides so that you have a rough circle.
Pour the pecan mixture onto the middle of the circle and arrange them so they are not positioned on top of each other. Leave a good gap all the way around.
Sprinkle over the dark chocolate chunks.
Carefully turn over the edges a bit at a time, pushing a little to the sides. Pat down gently so that the pastry sits in place. This does not have to be perfect - galettes are supposed to be rustic!
Carefully move the baking sheet, with the galette, onto a baking tray.
Bake in the oven for around 25 minutes, until the pastry is golden.
Allow the galette to cool, then sprinkle the edges with icing sugar just before serving. Eat warm or cold topped with ice-cream or whipped cream. Enjoy!