In a medium shallow bowl, whisk together the flour, salt, and sugar. Cut the butter into small 1/2" cubes, and add the cubes to the flour mixtures. Cut the butter into the flour using a pastry blender until the butter is in pea-sized pieces. Try to work as quickly as possible - you don't want your butter to start to get too warm.

Start adding the ice water to the crust mixture a tablespoon at a time, mixing after each addition. You want the crust to just be able to come together when you're stirring, probably with some floury crumbs still at the bottom of the bowl. I needed 3 tablespoons but every time is different. Try not to add too much water.

Dump the crust out onto your counter that's been lightly floured. Press the dough until it just comes together into a cohesive ball. Again, try not to touch it or work it too much. Wrap the ball of dough tightly in plastic wrap and refrigerate while you assemble the filling.

Combine the strawberries, rhubarb, both sugars, flour, tapioca, lemon juice, and salt in a bowl. 

Preheat the oven to 400°F and prep a baking sheet with parchment paper. 

Remove the pie dough from the fridge and cut it into 8 equal portions. While you assemble each galette, you'll want to keep the rest of the dough wrapped up back in the fridge. Roll out the dough portion into a circle that's about 6 inches across. If you want your galettes to have smoother edges, use a bowl as a guide to trim the edges. Spoon 3 tablespoons of filling into the center of the dough circle and gently fold the dough part way up the filling. Place on the prepped baking sheet. Repeat with the remaining dough pieces. 

In a small bowl, whisk the egg with 1 teaspoon of cold water. Brush the egg wash over the galettes and sprinkle with turbinado sugar. Bake for 20-25 minutes, or until the crusts are golden and the filling is bubbling and looks set. Let rest on the baking sheet for 10 minutes before serving with whipped cream. Enjoy!