Preheat your oven to 400F. Combine flour, ½ teaspoon of salt and ½ teaspoon of sugar in a food processor (hand mixer works fine if you don't have a food processor). Add butter and mix until the mixture looks crumbly, with the butter the size of small peas. Add 1 tablespoon of water at a time, pulsing until mixture starts to clump together. When you are able to pinch the dough and it holds together, it's done.
Remove dough from the mixer and place on a clean, lightly floured surface. Gently shape and knead the dough into a disk. Don't over do it. You should be able to see little bits of butter through out the dough. Wrap the disk in plastic wrap and refrigerate for half an hour.
Right before pulling your pie dough from the refrigerator to roll out, make your pie filling. In a medium bowl, mix together the blackberries, ½ cup of sugar, tablespoon of flour and pinch of cinnamon.
Gently fold the blackberries until it is all well incorporated. Feel free to substitute the blackberries for any other berry. Place in the refrigerator until ready to pour into the rolled out pie crust.
Remove the disk from the refrigerator and remove the plastic wrap. Over a lightly floured surface, roll out the dough to a 10-12 inch circle. Make sure your dough is not sticking to the surface, add flour as needed.
Transfer to a parchment lined baking sheet. Then, dump the blackberry mixture into the center or the dough and spread it out evenly leaving a 1-2 inch crust. Fold the edges of the pie crust letting it fold where it wants to.
Sprinkle a pinch of sea salt over the black berries. Make an eggwash in a small bowl using 1 egg yolk and 1 teaspoon of water. Brush the egg wash over the dough for a shiny and golden crust.
After brushing on the egg wash, sprinkle a little bit of whatever left over sugar is left from the filling along the crust.
Place that bad boy in the oven for 30 minutes. While it's baking, go ahead and make your whipped cream. I suggest making a double batch because you will eat half of it with a spoon, or so I've been told.
Now to make your whipped cream. Combine all three ingredients using a hand mixer or stand mixer. Mix until stiff peaks form. Do not over mix.
Wait for the galette to cool completely, sprinkle lemon zest over the top and then add a big dollop of the whipped cream over your slice of galette and enjoy!