Line a medium sized baking sheet with parchment paper. Set aside. To make the crust: Place flour into a mixing bowl with the sugar and salt, and add the paddle attachment. Give the flour, sugar, and salt a quick mix. Slowly add the butter cube by cube, and mix on low until it forms a wet-sand-like consistency. Alternatively you can use a pastry cutter and cut the butter into the flour mixture. Add the cold water one tablespoon at a time. Dough is ready when it is firm and not sticky. 

To make the cheesecake filling:  With a mixer or by hand, beat the cream cheese until smooth, about 20 seconds. Add the sugar and continue to mix until combined. Add the heavy cream and vanilla, and mix again. Add the egg and mix until just incorporated. Set aside.  To make the fruit filling: combine all ingredients into a bowl and toss until incorporated. 

Roll dough out on flat surface that has been dusted with flour. Roll out in a circle that’s about 12 inches wide all around. Place dough on parchment lined baking sheet. Gently fold about 2-3 inches of the edge up to create a barrier for when you pour the cheesecake in, pinches the edges together so it doesn’t fall. Pout cheesecake in the middle, and gently pour blackberry mixture over cheesecake mixture. leaving about 3 inches of the edge for folding. Gently move around the crust and fold it over the cheesecake and blackberries, leaving the middle of the galette open. Keep folding the next part on top of the previous part, and so on until the entire crust is folded inward. Brush crust with egg wash. 

Bake at 350° for 30-35 minutes, or until middle is mostly set and edges are a nice golden brown. Allow to cool completely on the counter or in the refrigerator before serving.  Top with whipped cream and powdered sugar if desired. Served 6-8. Store covered in the refrigerator for up to four days. Enjoy!  Alternate fruit-only galette: if you wish to omit the cheesecake portion and have only blackberries in this galette, simply double the fruit filling mixture, omit the cheesecake filling, and bake as directed.