Make the Crust:  Combine flours and salt in the work bowl of a food processor and process to combine.  Scatter butter cubes over the top of the flour mixture and pulse until mixture resembles coarse sand with a few pea-sized pieces of butter here and there, about 8-10 pulses.  Transfer mixture to a bowl and sprinkle the ice water over the top.  Mix with a fork and/or your fingers until no dry spots remain and the dough holds together when squeezed.

Transfer the dough to a piece of plastic wrap.  Gather into a ball and press into a disk, about 5 inches in diameter.  Chill for at least two hours or up to two days before rolling.

Preheat the oven to 375 degrees.  Transfer dough round to a piece of parchment paper.  Dust the top of the dough round with flour to prevent sticking.  Using a rolling pin, roll into a 12 inch circle.  Trim the edges with a pizza wheel if desired.  Transfer to an inverted baking sheet leaving parchment paper in place. Place in the refrigerator for 20-30 to firm up slightly.

Meanwhile make the Filling:  Whisk sugar, lemon zest, salt and flour together in a medium bowl.  Gently toss in strawberries and rhubarb until evenly combined.  In a separate small bowl, whisk the egg and 1 tablespoon of water together to create an egg wash.

Remove dough round from the refrigerator and place the dough round and parchment inside the rimmed baking sheet.  Top the round with the filling, leaving a 1 ½ to 2 inch border around the outside.  Fold the border of the dough inward over the filling so that it covers the filling by about 1 inch, overlapping the dough every couple of inches.  Gently press the folds in the dough so they adhere.  Brush with egg wash and sprinkle with turbinado sugar.

Transfer the galette to the oven and bake until the crust is golden brown and the filling is bubbly, about 50-55 minutes.  Transfer the baking sheet to a wire rack to cool.  Brush the fruit filling with the warm strawberry jelly or jam.  Cool to room temperature before serving.