Preheat the oven to 400 °F and line a sheet pan with parchment.
Unroll dough on a lightly floured counter and use a five-inch bowl to stamp out rounds. Transfer to the pan.
In a medium bowl, toss frozen blueberries, sugar, cornstarch, lemon zest, and juice in a bowl until the berries are coated.
Spoon blueberry mixture onto the center of each crust, leaving a one-inch border, then fold edges over the filling and pleat.
Brush crust edges with egg wash and sprinkle with coarse sugar (optional). Bake for 20-22 minutes until crust is golden brown and juices bubbly.
Let galettes rest five minutes so the filling sets before serving warm with yogurt or ice cream!
Notes
Mix filling just before baking: Combine the berries and sugar right before you assemble the galettes, so the fruit doesn’t have time to release extra juice and soften the crust.
Storage: loosely cover and enjoy within 12 hours, refrigerate up to 3 days and re-crisp at 325 °F for 6–7 minutes, or freeze baked galettes up to 2 months.
Serving ideas: Enjoy the mini galettes warm with a spoonful of vanilla Greek yogurt for extra protein, a small scoop of ice cream for a classic à la mode touch, or a dollop of whipped cream finished with a pinch of fresh lemon zest!