In a stand mixer bowl, combine flour, sugar and salt. Mix with the paddle until well combined. Add cubed, cold butter and mix on medium for about 90 seconds, until the texture resembles sand.

Remove the bowl from the stand mixture. Add water in increments, stirring with a wooden spoon until a dough just comes together. You do not want to over add the water.

Once a dough has come together, form it into a ball by hand (do this quickly so as not to melt the butter), wrap in plastic wrap, and chill for at least an hour.

Meanwhile, preheat the oven to 400 degrees (375 if using a convection oven) and prepare the rhubarb and strawberries.

Place the fruit in a bowl and stir in the lemon juice. In another bowl, combine the white and brown sugars, cornstarch, and flour. In yet another small bowl, whisk the egg yolk with ½ tablespoon water.

Once the crust has chilled, remove and roll out on a floured surface to a circle, about 14 inches in diameter. Place on a parchment lined baking sheet (I like to fold the dough in half and then in quarters to transfer it from the table to the baking sheet).

At this point, stir the sugar mixture into the fruit. Pour the fruit onto the center of the crust, leaving about three inches of dough on the edges. Gently fold up each edge, doing approximately 7-8 folds. Brush the edges of pastry with the egg wash and sprinkle a bit of sugar onto the crust by hand.

Bake for 35-40 minutes, until the crust is golden brown the bottom is cooked through. Allow to cool and set before serving.