Preheat your oven at 375° F. Prepare a jelly roll baking sheet with parchment paper, lightly dust with flour.
Slice strawberries and rhubarb. Place both into a large bowl and cover with the juice of the lemon. Mix with a large spoon. Add granulated sugar and continue to mix. Set mixture aside.
On a floured surface, roll your pie dough out into a large circle, about ⅛" thick and over a foot wide. Cut off the edges of the dough to make it even. You can add that dough into the center and push out from there to create an even circular shape (may be more oval). Place rolled out dough onto your parchment paper/baking sheet.
Drain the strawberry rhubarb mixture (save the liquids for fun summer cocktails/drinks). Use mixture to fill in the dough. Create a mound of strawberries and rhubarb in the center of the dough. About 1-2 inches away from the edge.
In a small bowl mix egg and water to make your egg wash.
Roll up edges of the galette around the mound of strawberries and rhubarb. Pinch and fold over as needed. You want this pretty tight and folded over so it doesn't fall and bake flat. Use egg wash with a pastry brush as an adhesive when needed. Then brush the entire dough top with egg wash. Sprinkle egg wash with extra granulated sugar.
Place in the oven and bake for 35-45 minutes. Until crust is golden brown.
Remove from oven and allow to cool.
When ready to serve: dust with powdered sugar, cut with a pizza cutter, and serve with a heaping scoop of ice cream.
Notes
- Filling: I don't tend to use corn starch in my pies and galettes. I know it helps to bind the juices, but the texture afterwards it isn't usually what I like texturally. However, if you are looking for that binder you can add about 2 tablespoons of cornstarch in with the lemon juice and sugar.