Begin by mixing together flour, salt, and sugar in a large bowl. Then, grate butter into the dry ingredients using a cheese grater.
Add sourdough starter and ice water to the bowl, and gently mix everything until small balls form. Transfer the dough to a clean work surface and gather it together into a ball.
Divide the dough in half and flatten each half to form two disks (which will make total of 2 galettes). Cover both disks with plastic wrap and refrigerate them for around 30 minutes.
Once chilled, roll out the dough on a lightly floured parchment paper to create a rough 12” circle.
Evenly spread a thin layer of strawberry jam on top of the dough, leaving a 2” (5cm) border around the edges.
Add wild blueberries and sliced fresh strawberries on top of the jam. Gently fold the edges of the dough over the filling, overlapping the dough and pressing to seal the edges.
Brush the crust edges with egg wash and sprinkle the crust and the filling with sugar.
Refrigerate the shaped galette for at least 15–20 minutes before baking it at 400°F (200°C) for 35-45 minutes, or until golden color. Enjoy your delicious and homemade galette!
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Notes
Use cold butter: It's important to use cold butter for the crust as it ensures that the dough is flaky. Cut the butter into small cubes and freeze it for at least 15 minutes before using it.
Chill the dough: After mixing the dough, it's important to chill it for at least an hour before rolling it out. This helps relax the gluten in the dough and makes it easier to work with.
Use parchment paper: Roll out the dough on a piece of parchment paper. This makes it easier to transfer the galette to the baking sheet without it breaking apart.
Bake on a preheated baking sheet: Preheat a baking sheet in the oven before baking the galette. This ensures that the bottom of the crust gets crispy and doesn't become soggy.