In a food processor, combine the gluten free flour blend, xanthan gum (if using), sugar, baking power, and salt. Pulse to combine.

Then add the very cold butter and shortening to the food processor. Pulse until the butter is the size of peas.

Place the flour/butter mixture in a large bowl.

Add the water, tablespoon by tablespoon, until the dough is able to be pinched together. You may not need the full 3/4 cup of water. If you need additional water, add one tablespoon at a time until your pie dough comes together.

Form the dough into a ball on a piece of parchment paper.

Then, refrigerate for at least and hour.

In a large bowl, mix together strawberries, rhubarb, granulated sugar, lemon juice, vanilla, salt, and cinnamon.

Let sit for at least 45 minutes to let the juices release.

Carefully drain the juices from the bowl.

Then stir in the cornstarch until combined.

Take the pie dough out of the refrigerator.

Slice the dough in half so you have two equal sized portions.

Generously flour a surface or parchment paper with gluten free flour.

Take one of the pie dough portions and roll it out to a round 1/8 inch thickness about 3 inches wider than your pie plate. So, if your pie plate is 9-inches, you'll want your dough round to be 12 inches in diameter.

Repeat with other pie dough portion, keeping the dough, surface and rolling pin generously floured to make sure it does not stick.

Carefully transfer one of the rolled out pie crusts to a 9-inch pie plate. You should have about 1/2 inch overhang of dough.

Add 1 tablespoon of gluten free flour over the bottom crust to soak up any additional juices from the filling.

Then, pour the strawberry rhubarb pie filling over the bottom crust.

Carefully place the other pie crust on top of the filling.

Roll the edges of the overhanging pie crust under itself until it reaches the pie plate. This will give you a higher crust for crimping.

Crimp the pie crust as desired.

In a small bowl, whisk together egg and water until combined. Brush the egg wash over the pie crust with a pastry brush.

Make a few slits with a knife in the top crust to let air escape during baking.

Place the pie plate on a baking sheet for easy handling.

Bake at 400F for 55-60 minutes, until the crust is a golden brown and the filling is bubbling.

Let cool for at least 2 to 3 hours before slicing to make sure filling sets up.