- Combine flour, sugar, and salt in a food chopper, pulse for 5 seconds. Add cold butter and pulse until well blended. Gradually add up to 4 tablespoons of ice water, pulsing after each addition, then add ½ tablespoon at a time until the dough starts to come together.

- Place dough on plastic wrap, form into a ball, flatten, wrap it up, and freeze for 1 hour.

- Mix flour, sugar, and salt in a large bowl. Cut in cold butter with a pastry cutter or fork until there are no large chunks. Gradually add up to 4 tablespoons of ice water, mixing with a spatula after each addition, then add ½ tablespoon at a time until the dough starts to come together.

- Form dough into a ball, flatten, wrap in plastic wrap, and freeze for 1 hour.

- In a medium-large bowl, mix strawberries, rhubarb, brown sugar, sugar, lemon juice, and corn starch until well combined. Refrigerate until ready to use.

- Divide chilled dough into 4 pieces. Work with one piece at a time, keeping others chilled. Form dough into a ball, flatten it on parchment paper, place another sheet on top, and roll out to an 8-inch circle.

- Place strawberry rhubarb filling in the center, leaving a 1-inch border. Fold edges tightly over the filling to form a 6-inch diameter galette.

- Transfer galette with parchment to a sheet pan and freeze. Repeat with remaining dough and filling, placing each galette on the pan in the freezer.

- Preheat oven to 375°F. After at least 20 minutes in the freezer, brush galettes with egg wash (yolk mixed with water) and sprinkle turbinado sugar around the edges.

- Bake on the middle shelf until the crust is golden and the filling is bubbly, about 15-40 minutes, depending on how long they were frozen.