Filling:
Put all of your apple slices (substitute to pear, plum...) in a bowl and toss with a some sugar, sprinkle in a bit of cinnamon, and a apoonful of corn starch . Toss it all together and set the bowl aside.

Galette Pastry:
1 1/4 cups all-purpose flour
1/2 tsp. salt
1/2 cup chilled butter, cut into pieces (one stick)
3 tablespoons ice water
Put flour and salt in the bowl of a food processor and pulse to combine. Add butter and pulse until the largest butter pieces are the size of peas. Add water, one tablespoon at a time, pulsing to mix. The mixture won’t look like it’s holding together, but pinch it, and it should stick together.

Dump all the flour and butter pieces out onto the floured counter or board, and gather it and press it together into a disc shape.
Roll dough out into a large circle, making sure to add a bit of flour on top and underneath the dough occasionally to prevent it from sticking to the counter. Try to roll the dough as evenly as possible to about 1/8 inch thick. The circle doesn’t have to be perfect and if the dough starts splitting and tearing, just patch it together as best you can.

Now gently wrap the dough around the rolling pin and transfer it to the sheet pan. Now dump the apple right into the center of the circle and spread them out a bit.

Next, just fold the edges of the pastry over the apples, sealing any holes that appear along the edges as you go.

Finally, I beat one egg with a splash of water and lightly brush the pastry with the egg wash. Then I sprinkle a bit of sugar over the whole thing. This is optional, but it looks nice!

Now put the baking sheet with the galette into the preheated 400 degree oven and bake for about 35 minutes.