Homemade Pie Crust: Make dough for galette crust following recipe instructions. Shape into a disc, wrap in plastic wrap and refrigerate for at least 1 hour or overnight (if you make it ahead of time).
Make The Filling: In a medium bowl, combine strawberries, sugar, cornstarch, lemon juice and vanilla extract and toss with a wooden spoon or a rubber spatula. Set aside.
Preheat oven to 375°F/190°C.
Assemble Galette: Place a disc of dough in between sheets of parchment paper. Use a rolling pin dusted with flour, rolling outwards from the center of the dough with an even pressure to make a large circle, around 10-12 inches in diameter (1/8-inch thick). Remove the top sheet of parchment, then transfer the dough to a baking sheet lined with parchment paper.
Arrange the strawberries in an even layer onto the crust, make sure to leave about a 2-inch edge uncovered with fruits. Pour any remaining juices left in the bowl over the fruit. Fold the edges over the berries and press slightly to seal them together.
Stir the egg in a small bowl with a fork to create an egg wash. Use a soft pastry brush to lightly coat the folds of the dough, then sprinkle with coarse sugar.
Bake the galette for 35-40 minutes or until the crust is golden brown and the fruit is bubbling. Remove the galette from the oven and let it cool before slicing.
Slice and serve galette warm with ice cream or whipped cream if desired. Enjoy!