CRUST
Combine flour, sugar, butter and shortening in the basin of a food processor and pulse to combine.
Slowly add water 1 TBSP at a time until dough forms a ball.
Transfer to a piece of lightly floured Parchment Paper and form into a ball. Lightly flatten into a disc and chill for at least 30 minutes and up to 2 hours in the refrigerator.
FILLING
While galette crust is chilling, preheat oven to 400F (205C) and prepare your fruit filling.
Combine fruit, sugar, lemon juice, and cornstarch in a large bowl and stir until well-combined. Set aside.
ASSEMBLY
Once dough has finished chilling, remove from refrigerator and open parchment paper. Lightly floured surface of the dough. Dust with additional flour and roll out to a 12-13” circle. Transfer to a baking sheet on the parchment paper.
Prepare egg wash by whisking together egg and water in a small bowl. Use a pastry brush to lightly brush your pie dough with egg wash (this will help keep the galette from getting soggy). Don’t discard egg wash yet.
Give your fruit one more stir in the bowl and then carefully transfer to the center of your galette crust, leaving a 2” perimeter of fruit-free crust.
Fold the perimeter/border of your crust carefully over the fruit filling and pinch together to secure (it will not completely cover it, you should have a nice circle of exposed fruit in the center!).
Brush the folded-over pastry with egg wash and sprinkle with sugar, if desired.
Transfer to 400F (205C) oven and bake for 30-35 minutes or until the fruit is bubbling and the crust is a nice golden color. Allow to cool before slicing and serving.