In a food processor, add flour and butter and pulse it until it's crumbly (about 15 seconds)
Add in the egg and water and pulse for another 15 seconds. It will form a dough once it's done.
* Make sure the butter and water are cold to make sure you get the flaky texture of the galette.
Place the dough between 2 parchment paper and roll the dough out to a 12inch circle. Refrigerate it for about 1 hour.
In the meantime, melt the chocolate over a double boiler and let it cool until it's in a spreadable consistency.
In a separate bowl, combine the berries of your choice with cornflour. Set aside.
Preheat the oven at 425F.
Remove the dough from the refrigerator and spread a layer of chocolate to the dough, leaving about 2.5 inches around the border. Top the berries on to the chocolate spread.
At one edge of the dough, fold the sides up, creasing it as you go until you get a nice pattern all around.
Brush the sides with some egg wash and sprinkle some sesame seeds or almond flakes.
Bake it for about 25 minutes until the edges are golden brown.
Remove from the oven, let it cool for about 10 minutes and then serve it while warm