Prepare Fruits: Wash and hull strawberries, chop into small pieces. Combine with blueberries, sugar, cornstarch, cinnamon, and lemon zest. Toss gently until well-coated and sugar begins to dissolve. Set aside.

Roll Crust: Let premade pie crust sit a few minutes. Roll out to about 1/8 inch thick. Cut circles with a bowl approximately 4.5 inches in diameter. Gather trimmings, re-roll, and cut more circles as needed.

Assemble Galettes: Preheat oven to 375°F (190°C) and line baking sheet with parchment paper. Place about 1/4 cup fruit mixture in the center of each dough circle. Fold the edges up around the filling to create a rustic tart shape.

Finish and Bake: Brush edges with egg wash, sprinkle sugar over crust. Transfer to baking sheet, leaving room to expand. Bake for 25-30 minutes until crust is golden brown and filling bubbles.

Serve: Let cool slightly on a wire rack. Serve warm or at room temperature, optionally topped with whipped cream or vanilla ice cream.