Place the flour and salt in the bowl of your food processor and pulse to mix.
Add the very cold butter, cut into small cubes, and slowly pulse to blend it into the flour until you get a thin crumb like consistency.
While pulsing, slowly add the very cold water a little bit at the time. Stop as soon as the dough comes together, transfer over a sheet of baking paper on your kitchen bench.
Assemble the dough into a ball and gently flatten it with your hands. Place a second sheet of baking paper over it, and leave to rest for about 10 minutes.
Roll the pastry into a large circle, place the tart pan over it, to check it is rolled wide enough to fill it.
Place the rolled pastry over a flat tray and leave in the fridge to rest for at least 1 hour.
Assembling the Galette
Add goat cheese in crumbles in the first layer. Top with alternating slices of sweet potato and apple.
Fold tart dough about an inch into the filling, overlapping the previous fold.
Brush the dough with a whisked egg. Top with black pepper.
Bake 45 minutes until crust is golden brown.
Serve with fresh thyme and reduced balsamic vinegar.
