In the bowl of a stand mixer, place your room temperature butter. Sift the whole wheat flour, all-purpose flour, and salt together, then add them to the butter.
Mix on low speed just until the are combined. Be careful not to overbeat.
Add the cold water and continue to mix on low speed just until the dough comes together into a single mass. Again, do not overmix, or the gluten will develop and create a tough crust.
Turn the dough out onto a work surface, weigh it, and divide it into two equal pieces.
Place each piece on a sheet of plastic wrap, flatten it into a 1/2-inch thick square, and wrap it tightly.
Refrigerate for at least 2 hours, but preferably overnight.
When ready to bake, lightly butter two 9-inch tart pans.
Roll out one disc of chilled dough and line a pan. Use a fork to pierce holes (dock) the bottom of the crust every inch or so to allow steam to escape.
Refrigerate the lined pan, uncovered, for several hours or overnight.
Repeat with the second disc of dough.
To blind bake the crust, preheat your oven to 325°F (165°C).
Place a sheet of parchment paper inside the chilled tart shell and fill it completely with pie weights, dried beans, or uncooked rice.
Bake on a sheet pan for 15 minutes.
Carefully remove the parchment and weights. Return the crust to the oven and bake for another 15 minutes, or until it's a light golden brown with no signs of moisture.
Let it cool completely before filling.
Do not overmix the dough.
Mix only until the just come together to prevent developing gluten, which results in a tough, not tender, crust.
