Preheat oven to 400℉
Remove the dough from the freezer/refrigerator. Place on parchment paper. Sprinkle with flour as needed to prevent sticking while rolling dough out into a 13"-14" round.
Transfer Parchment + Pastry onto a large baking sheet.
Spoon the Berry/Rhubarb mixture into the middle of the pastry round. Spread out to about 1.5" from the edge - leaving enough pastry to fold back towards the center.
Carefully fold the edge over the filling, pleating it at about 2 inch intervals.
Dot the filling with the cut up 3 Tablespoons of butter.
Using a Pastry Brush, brush the cream over the pastry crust.
Sprinkle the Turbinado Sugar over the brushed cream.
Bake the Galette for 45minutes - 1 Hour, or until the fruit is bubbling and the pastry is golden brown.
Let cool a bit before slicing. Enjoy!