Preheat the oven to 400˚F. Line a baking sheet with parchment paper.
Slice the strawberries and combine with the blueberries in a bowl. Set aside.
Combine the sugar, corn starch, cardamom, and water in a medium pot over medium heat. Stir until the mixture begins to thicken.
Add the strawberries and blueberries to the thickened sugar mixture and toss to coat. Remove from the heat while you roll out the dough.
Remove the one disk of dough from the refrigerator, unwrap, and roll out into a circle about 7 - 8 inches in diameter. Place it towards one of the corners of the baking sheet. Heap some strawberry filling in the middle. It's fine if it spreads out. Carefully fold the edges of the dough towards the middle.
Brush a little cream on the edges of the crust and sprinkle a little turbinado sugar on top.
Repeat with the remaining disks of dough, forming each galette on the baking sheet.
Bake for 30 minutes, or until the crust is lightly browned and the filling is bubbling.