Pre-heat the oven to 400 F and cover a baking sheet with parchment paper.
Add the flour to a bowl and stir in the salt and powdered sugar.
Add the chilled butter into the bowl. Using a pastry cutter, cut the butter into the flour until the butter is the size of small pebbles. Using your fingers, continue to rub the butter into the flour until it becomes a sandy consistency.
Slowly add the iced water to the flour mixture and lightly knead until it forms a dough. If the dough is crumbly, continue to slowly add water, until the dough will form into a ball.
Leave the dough in the bowl, cover it with plastic wrap and chill it for at least 30 minutes.
Meanwhile prepare the filling. Add all of the blueberry filling ingredients to a sauce pan and bring to a simmer over medium heat. Stir and let simmer for 5-minutes and remove from heat. Let the mixture steep for an additional 30 minutes. Add all of the ingredients for the strawberry rhubarb filling to a bowl and set aside for 20 minutes, giving it a stir once or twice.
Bring the dough to room temperature before separating it into 6 small balls. Lightly flour a flat surface and roll each ball of dough into circles about 6 inches in diameter.
Once the dough has been rolled out, place each circle on the baking sheet. Fill the center of each circle with berry filling. Leave about an inch or more of dough around the filling and begin to fold it in, wrapping it around the fruit. Repeat this for each mini galette.
Brush the crust of each galette with egg wash and place it in the oven.
Bake for 20 minutes, or until the crust is golden brown and the filling is bubbling.