A simple and rustic fruit galette. The filling is adapted from Yossy Arefi's Sweeter Off the Vine, via Alanna Taylor-Tobin of The Bojon Gourmet. The crust is loosely adapted from Yossy Arefi's recipe on Apt. 2 Baking Co.
In a large mixing bowl, whisk the flour with the salt and sugar.
Add the cold butter and cream cheese chunks, and cut them in with a pastry blender until the size of small peas. Add the sour cream, and continue blending the mixture with the pastry blender until it just starts to clump together. Then, using your fingers and working quickly, gather the dough into one mass and transfer to a piece of plastic wrap.
Using the sides of the plastic wrap to help you (and to avoid warming the dough with your hands), press the mass of dough into a rough disk. Fold the plastic wrap around the dough and transfer the package to the refrigerator to chill for at least 2 hours.
Place an upside-down baking sheet (or a pizza stone) on a rack in the lower third of the oven. Preheat the oven to 425 F.
Remove the chilled dough disk from the refrigerator and turn it out onto a large sheet of parchment paper (floured lightly if you wish). Cover the disk with another large sheet of parchment, then roll out the dough between the sheets of parchment until you have a round about 1/8 inch thick.
Transfer the rolled out crust, still between the sheets of parchment, to a baking sheet and place it in the refrigerator to chill while you mix the filling.
In a small or medium bowl, mix together the sugar, salt, and cornstarch.
Place the chopped rhubarb and trimmed, sliced strawberries in a large bowl. Add the lemon juice and rose water. Add the sugar mixture and gently toss to combine.
Remove the baking pan with the rolled out pastry dough from the fridge, and carefully peel off the top sheet of parchment.
Quickly mound the fruit filling in the middle of the dough, leaving at least a 2-inch border around the edges. Fold the edges of the dough in and over the filling, pleating the crust to form a neat shape.
Brush the crust with the beaten egg, then sprinkle with turbinado sugar.
Place the baking pan with the galette in the oven, on top of the preheated pan or pizza stone.
Bake for 30-35 minutes, then check: the galette will hopefully by now be bubbling and possibly oozing lovely sticky strawberry-rhubarb juices. If the juices are bubbling out of the crust--all the better! Open the oven, and carefully spoon some or all of the bubbled-over liquid back on top of the galette filling. (This will form a lovely glaze.) Close the oven, reduce the heat to 400 F, and continue baking for about 15 minutes longer, checking every few minutes to see if more juices have bubbled out. If they have, just go back in and spoon them on top of the filling. When the crust has turned a golden, burnished brown, remove the galette from the oven and place the pan on a wire rack to cool.
As with all pie crusts, the key to the pastry here is to keep your ingredients cold, cold, cold. Sometimes I actually pop the whole bowl and pastry blender in the freezer for a minute after cutting in the butter and cream cheese, before adding the (cold) sour cream.
I've given a range for the amount of sugar because there are virtues to both a super-sticky, bubblingly sweet filling, and a tart, somewhat more staid, affair. Feel free to adjust to taste.