In a large bowl, whisk together the all-purpose flour, 1 tablespoon granulated sugar, and 1 teaspoon salt.

Add the cold butter cubes to the flour mixture. Using a pastry blender, your fingertips, or a food processor, cut the butter into the flour until the mixture resembles coarse meal with some pea-sized butter pieces remaining.

Gradually add ice water, 1 tablespoon at a time, mixing gently until the dough just comes together. Be careful not to overmix. You might not need all the water, or you might need a little more.

Divide the dough in half, flatten each half into a disc, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes, or up to 2 days.

In a large bowl, combine the sliced strawberries and chopped rhubarb.

In a separate small bowl, whisk together the 3/4 cup granulated sugar, cornstarch, and a pinch of salt.

Pour the sugar mixture over the fruit. Add lemon juice and vanilla extract. Gently toss until the fruit is evenly coated. Set aside for 15-20 minutes to allow the fruit to release some juices.

Preheat your oven to 400°F (200°C). Place a baking sheet on the bottom rack of the oven to catch any potential drips.

On a lightly floured surface, roll out one disc of pie dough into a 12-inch circle. Carefully transfer the dough to a 9-inch pie dish. Trim the edges, leaving a 1/2-inch overhang.

Pour the strawberry rhubarb filling into the pie crust. Dot the top of the filling with the small pieces of butter.

Roll out the second disc of pie dough for the top crust. You can either place it whole over the filling and cut vents, or create a lattice top.

If using a solid top crust, drape it over the filling, then trim the edges to match the bottom crust's overhang. Fold the top and bottom crust edges together, then crimp decoratively with your fingers or a fork to seal. Cut several slits in the top crust for steam to escape.

In a small bowl, whisk the beaten egg with 1 teaspoon of water to make an egg wash. Brush the top crust generously with the egg wash and sprinkle with turbinado sugar.

Place the pie on the preheated baking sheet in the oven. Bake for 15 minutes at 400°F (200°C).

Reduce oven temperature to 375°F (190°C) and continue baking for another 50-55 minutes, or until the crust is golden brown and the filling is bubbling thickly. If the crust starts browning too quickly, loosely tent the pie with aluminum foil.

Once baked, transfer the pie to a wire rack and let it cool completely for at least 3-4 hours before slicing and serving. This allows the filling to set properly.