Creating the French Nectarine Blueberry Galette can be straightforward if you follow these simple steps:

1. Make the Dough: In a large bowl, combine flour, salt, and granulated sugar. Cut in the chilled butter until the mixture resembles coarse crumbs. Gradually add ice water, stirring until the dough comes together. Form into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

2. Prepare the Filling: In another bowl, combine sliced nectarines, blueberries, brown sugar, cornstarch, and vanilla extract. Gently toss until the fruits are coated. Set aside to allow the flavors to meld.

3. Roll Out the Dough: On a lightly floured surface, roll out the chilled dough into a 12-inch circle. Transfer it to a parchment-lined baking sheet.

4. Assemble the Galette: Spoon the fruit mixture into the center of the rolled-out dough, leaving a 2-inch border. Fold the edges of the dough over the filling, pleating it as you go. Brush the crust with beaten egg and sprinkle coarse sugar over the top.

5. Bake: Preheat your oven to 375°F (190°C). Bake the galette for 30-35 minutes or until the crust is golden brown and the filling is bubbling. Allow it to cool for about 15-20 minutes before slicing.