To a bowl add the flour, salt, sugar, ad mix it. Add the cubed cold butter. With a pastry knife/blender, cut the cubes of butter incorporating tiny bits of it into the dough.
Sprinkle ice cold water as necessary to gather the dough into a ball. Wrap, and refrigerate for at least an hour.
Preheat the oven to 400℉
Take the dough and roll into a 11-in circle. Place the rolled crust on to a parchment lined tray. Alternatively, I prefer to roll the crust on a parchment itself and transfer it to a tray.
Add the sugar, corn starch, vanilla extract paste and lemon juice. Fold the nectarine with the mixture gently enough to coat the fruit.
Leaving about one and one and a half inch around, brush the pie dough with two-thirds of the cherry jam.
Arrange the nectarine slices in a appealing way (or as you like it) on the pie crust on top of the jam.
Fold the edges of the dough over the nectarine filling, overlap it if needed when making the fold in a circle shape making sure to press the edges to seal them. Brush with remaining cherry jam. Brush with milk and sprinkle with sugar.
Bake for 30-35 minutes at to 400℉ until the crust is golden and the filling is bubbly. Remove from the oven, cool for 10 minutes and then slice.
Serve the nectarine galette slice as such or with a scoop of ice cream.